As long as we're bumping...
I still hear the sound on cool-down...faint, not irritating or anything, BUT my battery does seem to run down, in fact it is dead currently after only a couple of weeks. My battery always runs down on the NSX. I use a trickle charger, which does the trick of keeping it ready (when I remember to plug it in), but I have many other vehicles that are started just as often and their batteries don't run down at all. Keep in mind, this is over many years of experience with many different batteries. Always wonderd...it seamed to have some kind of current leak running the battery down. This quote below from a post above (which i didn't notice 5 years ago -- time flies) notes that a solenoid is involved...presumabley battery powered...hmmm.
[From the service manual:
"When the fuel vapor in the tank is higher than the set value of the valve it opens and regulates the flow of fuel vapor to the canister. The canister purging is accomplished by drawing fresh air through the canister and into a port on the throttle body. The purging vacuum is controled by the purge control diaphragm valve and the purge cut-off solenoid valve. "[/QUOTE]