Chasing strange whine

[bruckner]

SOLVED: Chasing strange whine

This is sort of a repost which I had initially suspected to be associated with VVIS, a strange whine or drone noise coming from the engine bay at idle (even the slightest increase in RPM kills it) when the engine has been fully warmed up (sound clip is posted below).

The mechanic who recently worked on the car is very knowledgeable about the NSX and did a great job replacing the WP/TB and many other components, but he couldn't conclusively identify the provenance of this rather novel noise, other than saying it seems to be coming from the intake area or within the valley of the motor, characterized as a kind of turbulence harmonic or resonance. Anyone encountered this?

I inspected VVIS flaps, all are correctly screwed in and the flaps close as they should upon startup.

Alternator and a/c tensioner bearings were inspected and were deemed quiet, I'm also assuming a bearing noise would be heard at higher revs as well as idle, but I could be wrong. The noise doesn't sound metal/metal to my ears.

Any ideas appreciated, here is the sound clip:

https://youtu.be/I3YUQFXKCbU

 

[jwmelvin]

I wish I had a better idea, but in an attempt to isolate things, you could try disconnecting the intake or removing the air-filter cover.

 

[goldNSX]

Sorry to say but the video is horrible to watch. You should make a video with more light and with rpm blips. My first guess is that the TB has been tensioned a little bit to much but only slightly.

 

[bruckner]

Sorry to say but the video is horrible to watch. You should make a video with more light and with rpm blips. My first guess is that the TB has been tensioned a little bit to much but only slightly.

Thanks for taking a listen, but it should be approached as a sound file, not a video. I'm documenting a noise, visually it's no different than any other NSX motor, and like I said, the noise is heard strictly at idle, a rev blip no matter how small will kill the noise.

TB tensioner too tight is one of my concerns, I suppose it's a big job going back in there to alter the tension, and in the meantime too much tension would put extra stress on a bunch of components...

 

[goldNSX]

The problem is that the intensity of the noise varies depending on the location but when it's the loudest we only see a black hole.

 

[NSXGB]

Sounds to me like a bearing noise, maybe in the alternator? Try removing the belts to cancel that off the list?

 

[bruckner]

The problem is that the intensity of the noise varies depending on the location but when it's the loudest we only see a black hole.

Gotcha. Sound clip starts on the airbox side, halfway through moves to the belt side.

Apparent consensus on bearing noise, the mechanic who inspected the car when it was brought back to him to investigate the noise said bearings (alternator and ac tensioner) were looked at before reassembly and were fine (though it must be said were not new, unlike the TB tensioner bearing which was a new part), which is why I sort of canceled those off the list, but I don't know whether he effectively took the belts off to determine whether these had anything to do with my strange and annoying noise.

Crossing fingers this external and not TB deep...

 

[MotorMouth93]

Remove the alternator belt and see if the noise goes away.

Remove the AC belt and see if the noise goes away.

Definitely sounds like bearing noise.

 

[Old Guy]

I am an old guy and my hearing isn't what it used to be. I also am not sure that I am listening to the correct noise; but, what I hear sounds more like a resonance / drone associated with air movement. Like something in an air duct in an HAVC system. I suggest that with the engine running, remove the air filter cover, give a listen and then remove the air filter and listen again to try and ascertain whether the noise is originating from inside the intake air duct or intake manifold. A bit of a long-shot; but, doesn't cost anything to try although it is not immediately obvious what would be making the noise in the air duct.

Removing the alternator belt and then running the engine would definitively eliminate the alternator bearings as a source of the noise. The only thing I am thinking is that you may want to disconnect the electrical connections to the alternator when you do this. If the alternator remains electrically connected the voltage regulator will monitor the DC voltage and attempt to raise it to the normal value of around 14 volts by controlling the alternator field current. Because the alternator is not turning the DC voltage remains stuck at 12 volts so the regulator will push the alternator field current to its maximum limit attempting to get the voltage up to 14 volts. This much higher than normal field current will cause some alternator field heating and the brushes will not 'like' high current when they are not spinning (worst case the brushes could stick to the slip rings). This may not cause immediate failure of the alternator; but, would definitely push the ageing process along a bit. If you leave the alternator connected and you are real quick with the test, the accelerated ageing may not be an issue.

As an observation a running alternator test may not be necessary. If you remove the alternator drive belt and then manually spin the alternator; a deteriorated bearing will usually become evident. Check for in - out movement of the alternator shaft. The sound I hear does not sound like the rattling that can occur when the shaft is moving back and forth; but, that type of noise can disappear quickly with RPM when one of the forces causing the back and forth movement 'wins over' and holds the shaft in one position eliminating the noise.

 

[Jerry@Mobile]

I think it's the alternator. I had the same whine and narrowed it down to the alt. It was not the bearings going south, it was a diode. I took the alt. to an old school rebuilder. He hooked it up and ran it on an old DC motor and you could hear the whine. Since the part had 65 K on it, the shop put in new bearings, brushes, diodes etc Back the same day for about $80. Jerry

 

[topolone]

sent you a PM , check if you have received

 

[bruckner]

PROBLEM SOLVED.

As a followup to this thread of mine, it could be of use for the community to know what caused this odd noise. It was an insanely loose timing belt.

https://youtu.be/43l2Ur4epRI

To recap, I had the TB/WP service done late last summer and the car was returned to me producing the noise documented in the first post. After sending the video to the technician who did the work, he asked to inspect the car but couldn't find anything wrong with it, well that's just because he didn't look hard enough. The car went into winter storage and of course made the same very annoying noise when I took it out last month. Since the first mechanic couldn't find the issue, I brought the car to a VW/Audi/Porsche technician who isn't specialized in NSX but accepted to install a new alternator in my car, but when he found out I was asking to have the alternator replaced as a potential fix to this noise, he suggested it was a more serious problem, and indeed taking the belt off proved him right as the noise was still present. I made another appointment and brought the car back to him, within an hour he had the alternator, A/C and TB covers off to uncover the problem and performed the tensioning sequence as per the workshop manual, what evidently wasn't done correctly in the first place, nearly ruining a very hard to replace motor.

The mechanic who changed the TB in the first place has been notified of the problem about 2 weeks ago. I am still waiting for his response.

 

[Old Guy]

That qualifies as a WOW. That one didn't even enter into my consideration as a possibility.

After tensioning, did they check the timing marks to insure that the belt hadn't hopped a tooth. I assume the resonance noise was the belt fluttering. Is there any evidence that the belt was hitting the cover because of the flutter?

If the work was done at a dealership I would be inclined to go back to them and request that at the very least they cover the cost of your visit to the VW / Audi tech.

 

[bruckner]

That qualifies as a WOW. That one didn't even enter into my consideration as a possibility.

After tensioning, did they check the timing marks to insure that the belt hadn't hopped a tooth. I assume the resonance noise was the belt fluttering. Is there any evidence that the belt was hitting the cover because of the flutter?

If the work was done at a dealership I would be inclined to go back to them and request that at the very least they cover the cost of your visit to the VW / Audi tech.

Timing marks were double checked before re-assembly, the whole operation of getting to the TB, setting tension and reassembly took about 5 hours. The Audi tech said I was one monkey shift at high RPM away from jumping a couple teeth wrecking the engine. In fact, when bringing the car to him for the first time to swap alternators, he listened to the noise and recommended I didn't drive the car until he had the time to dig deeper and find the issue, whereas the first mechanic who did the TB job returned the car to me after investigating the noise and said it was fine; of course we know now it wasn't.

The Audi tech didn't report evidence of the t-belt rubbing onto the cover, although he may not have looked specifically for this.

I sent the video of the loose belt to the mechanic 2 weeks ago, I'm still expecting a response. I had chosen his service because he had done many NSX t-belt jobs and was recommended by a friend who has his own NSX serviced with him. Sounds like reasonable logic, right?! Now I think a fresh mind following steps diligently probably has a better chance of performing the job correctly than someone doing a repetitive routine job. I am obviously very disappointed about this costly event and troubled that the mechanic has not yet bothered to respond and offered to make it right. I will wait a little more, but if he won't take responsability for his mistake on top of making it in the first place (and given a chance to find and fix the issue before taking a car to someone who quickly identified and fixed the problem), I will at least let the local owner's club know about this.

As far as the broader community is concerned, we now know what a crazy loose timing belt sounds like.

 

[goldNSX]

Thanks for the update, that was very educational. Now you have a good story for the next team gathering.

 

[drew]

The TB on the NSX is extremely difficult. It is why a lot of shops require engine removal or they decline the job.

It's one of those jobs where you do it yourself and it takes 20+ hours.

OR

You employ some of the very few techs with a known track record of replacing the TB without issue.

If you have to fly out the tech or ship the car across country: it is well worth it.

Had the belt slipped it would be a $6K-$10K job and the prior mechanic would disavow any responsibility.

**

Now, what I don't understand why the previous mechanic didn't pull the accessory drive belts for diagnosis. It's a 30 minute job and gives a clear indicator of where the problem lies.

Instead he spent a lot of time justifying some sort of harmonic wind phenomena. Very strange. This shop should probably be named.


I've done the TB job. I spent hours verifying everything over and over again. I went and purchased additional mirrors and straight edges TWICE. Kaz was even kind enough to give helpful advice too.

I had driven my car for years on a TB that was TWO teeth off--rear and front cam off by one. It's easy to do and caused no harm. (this mechanic also wrote up a "snap ring repair" that I later found out to be the simple replacement of the actual snap ring and not the transmission housing...which I also later performed myself when it failed).

 

[bruckner]

The TB on the NSX is extremely difficult. It is why a lot of shops require engine removal or they decline the job.

I may point out that the TB job that resulted in the loose belt was done with the engine OUT. The Audi mechanic who fixed the timing and tensioned the belt properly did it with the engine IN.

Now, what I don't understand why the previous mechanic didn't pull the accessory drive belts for diagnosis. It's a 30 minute job and gives a clear indicator of where the problem lies.

Instead he spent a lot of time justifying some sort of harmonic wind phenomena. Very strange. This shop should probably be named.

That's how I feel. The Audi technician figured out the problem within an hour and upon hearing the noise he thought it was a serious issue that had to be investigated in the TB area.

In fairness I'll give the guy (an NSX expert) time to respond before revealing his name. Two weeks have passed and I haven't heard from him, he was the first person I sent the video to and I know he's aware of the issue. From hearsay he blames his assistant for the error, which would be just as unacceptable (I brought the car to him not his assistant), and I returned the car to him to investigate the noise, he couldn't find anything wrong with it. Everything is wrong about this story, and indeed had the timing slipped we would have never known for sure what caused the bomb to go off.

 

[drew]

> The Audi mechanic who fixed the timing and tensioned the belt properly did it with the engine IN.

I'd say if there anybody that can figure out the NSX TB without experience would be an Audi Tech.

They are seasoned to extreme over-engineering, crazy complicated service procedures, and require extreme attention to detail as Audi's are an challenging vehicle to service. Modern Audi's do take the trophy for most difficult to replace cam timing systems.

**

As for blaming the assistant: that is cowardly. The head of the operation represents all their employees.

And worse, the service item was returned for an anomaly that should have had serious consequences. The head of the operation did not conduct even the most cursory of quality assurance, for an expensive and critical service, and deemed a previously unknown phenomena as the cause.

And an optional engine-out procedure was performed too, there should be no excuses.

Too many red flags.

I always like to audit my work and look forward to continuous process improvement; it makes me happy.

 

[Miner]

Unbelievable.

It looks as if the tensioner was still in the fully loose (installing the belt) position and was never adjusted to tension the belt (bar the engine over in opposite rotation, etc). Very fortunate it didn’t jump teeth.

The previous shop should gladly pay for the repair, and be thankful it is only 5 hours of labor.

 

[drew]

>In fairness I'll give the guy (an NSX expert)

In reality let's call him an NSX "professional".

A professional does it for a living, it does not mean they know what they are doing.


/I missed this and had comment on it.

 

[goldNSX]

Sh*t happens. It might be an exception, if not I'd be worried about all other TBs the shop worked on. I'd inform the local Canadian group anyway, 2 weeks with the head in the sand is too much. I still think it's one of these outliers that CAN happen.

Audi cars : they attract the most talented mechanics because they NEED them to repair those shitty cars. No wonder, he did it in 5 hours. If you worked on Audi you're able the repair a Space Shuttle. :wink:

 

[Old Guy]

Audi cars : they attract the most talented mechanics because they NEED them to repair those shitty cars. No wonder, he did it in 5 hours. If you worked on Audi you're able the repair a Space Shuttle. :wink:

You are not making me happy :frown:. I have tired of the lumbering SUV experience and want to go back to a station wagon for hauling my 17' kayak and other stuff around. I had pretty much zeroed in on the Audi A4 Allroad being the only station wagon option available in North America (current Volvo wagons having execrable reliability levels). Europeans and the Brits have a much better selection of wagons including nifty versions based upon the Honda Accord and Mazda 6.

 

[bboxer]

Goldnsx, Sometimes it is just exaggeration. With that in mind I bought a new 2014 Audi RS5 for daily driving. 5 years and 42K miles (some hard miles), I can report two problems only: front rotors warped early at around 8K miles, replaced with new pads under warranty. A faulty O2 sensor, also replaced under warranty. The rest has been routine scheduled maintenance (covered by Audicare)..... yes sometimes it is exaggeration that taints a product....or maybe I got lucky.

 

[Honcho]

PROBLEM SOLVED.

As a followup to this thread of mine, it could be of use for the community to know what caused this odd noise. It was an insanely loose timing belt.

To recap, I had the TB/WP service done late last summer and the car was returned to me producing the noise documented in the first post. After sending the video to the technician who did the work, he asked to inspect the car but couldn't find anything wrong with it, well that's just because he didn't look hard enough. The car went into winter storage and of course made the same very annoying noise when I took it out last month. Since the first mechanic couldn't find the issue, I brought the car to a VW/Audi/Porsche technician who isn't specialized in NSX but accepted to install a new alternator in my car, but when he found out I was asking to have the alternator replaced as a potential fix to this noise, he suggested it was a more serious problem, and indeed taking the belt off proved him right as the noise was still present. I made another appointment and brought the car back to him, within an hour he had the alternator, A/C and TB covers off to uncover the problem and performed the tensioning sequence as per the workshop manual, what evidently wasn't done correctly in the first place, nearly ruining a very hard to replace motor.

The mechanic who changed the TB in the first place has been notified of the problem about 2 weeks ago. I am still waiting for his response.

This is shocking as it is disappointing. Really no excuse for failing to tension the timing belt.

Unbelievable.

It looks as if the tensioner was still in the fully loose (installing the belt) position and was never adjusted to tension the belt (bar the engine over in opposite rotation, etc). Very fortunate it didn’t jump teeth.

The previous shop should gladly pay for the repair, and be thankful it is only 5 hours of labor.

I think that's exactly what happened. He just installed the belt and did not tension it.

>In fairness I'll give the guy (an NSX expert)

In reality let's call him an NSX "professional".

A professional does it for a living, it does not mean they know what they are doing.


/I missed this and had comment on it.

Probably was moving too fast, though it seems rather unbelievable that one would forget to tension the belt. Even the NSX experts make mistakes. Both Kaz and LarryB have stories, but the difference is they stood behind their work and fixed the problem at no charge.

Sh*t happens. It might be an exception, if not I'd be worried about all other TBs the shop worked on. I'd inform the local Canadian group anyway, 2 weeks with the head in the sand is too much. I still think it's one of these outliers that CAN happen.

Audi cars : they attract the most talented mechanics because they NEED them to repair those shitty cars. No wonder, he did it in 5 hours. If you worked on Audi you're able the repair a Space Shuttle. :wink:

This made me laugh out loud. So true!

You are not making me happy :frown:. I have tired of the lumbering SUV experience and want to go back to a station wagon for hauling my 17' kayak and other stuff around. I had pretty much zeroed in on the Audi A4 Allroad being the only station wagon option available in North America (current Volvo wagons having execrable reliability levels). Europeans and the Brits have a much better selection of wagons including nifty versions based upon the Honda Accord and Mazda 6.

Maybe a gently used Accord Crosstour? Those are supposedly great wagons that never caught on in the states...

 

[goldNSX]

No offense to Audi owners. Audi makes good cars. They're very common here as they're favored by people in Europe how want the 'image factor' and pay 'premium' for it. But better sell them when the guarranty is over. These cars are over-engineered and as expensive as BMW to repair when they get older. Not the best low-term-owner car money can buy.
My love for Audi dates back to 1980-1988 but at that time Audi was in trouble in the US with their so-called 'self-accelerating' automatics (if that ever was the case or if people just confounded the two pedals). BTW, my very first 'virgin' attemps 30 years ago on wrenching was on VWs and Audis but (good old) times were pretty simpler then. After moving to Honda I was stroke by lightning about their long-term quality. After 6 years they started to require intensive care, rubber parts and more. When you thought you've went through all of it and have left it behind you it started all over again with the same parts and more... At least my wrenching technique got better and better...