That 99% sounds like the bearings on your AC idler pulley being worn out.
If you check the load on your battery it's probably going to be charging just fine which will rule out the alternator (plus your car is probably driving fine).
With some listening equipment you can isolate where that whine is coming from just to make sure (or use a long pole and carefully touch the nut of each pulley while the engine is running and isolate it from there).
And like it says, you don't have to replace the entire assembly nor take it all out.
The bearing's listed as well --> https://www.amazon.com/dp/B000UVKERI/ref=cm_sw_r_cp_api_glc_fabc_YJG7Fb5WZW3S8?_encoding=UTF8&psc=1 and your local bearing supplier will most likely have it in stock (or something comparable) if they don't carry NTN. There are cheap unnamed ones from China around $5-8 and high end ones for $13-14 (for ex. by SKF) and although it's just an idler pulley, go ahead and splurge so you don't have to deal with it again :smile: and like Kaz mentions just confirm it is a double seal & contact type bearing.
The only thing the thread doesn't cover is after the new bearing's on and you're reinstalling the pulley onto the assembly, you have to play around with the adjustment knob to get the tension on A/C belt just right (page in manual listed in the thread) just before torque wrenching everything down. And if you don't have a belt tensioner tool you can always use the poorman's 1/4 twist of a turn to get your in the ball park and the next time you bring it in you can just ask them to quickly double check it. All in all it is a less than $15 dollar repair and will take 1-2 hours of your day.