Originally Posted by RandyVW

Does it stop it for you when you try the foot on exhaust tip??

If it's truly a 100% on when A/C on and off when A/C off, I'd try to get a second ear in where you (or the 2nd person) can get their ear as close to the location of the noise as possible.......A/C on/off and/or foot on/off the exhaust tip.

(Another pro tip for finding sounds can be a short length of tubing (anything, even old garden hose) to hold from your ear to the motor as a stethoscope to pinpoint more closely where a sound is coming from. Especially when you don't want to get your head/ear/hair too close to a bunch of pulleys runnin' a belt under a serious horsepower.

Originally Posted by Bruce In Philly

2009 C2S 197K miles

It may be an exhaust leak. It was for me and happened in both side mufflers over time. The sound ... I can't really hear anything in that recording... but pressing on the muffler tips is a dead giveaway for a leak IMO. Pressing on the tips was my acid tests for discovering my leaks (each muffler, different years). Regarding the AC, the engine's computer compensates the throttle for the changing load and this could crest some sort of air volume threshold that you can hear/not hear... acoustics are really bizarre in these situation.

You can put a mirror up in there from underneath and you will see black carbon around the weld points (dead giveaway)... the muffler cracks/tears in only one place ... at least I never heard of any crack elsewhere than this one weld. Easy diagnosis.

IIRC, the first noise I heard was some sort of whistling sound that very slowly grew into a more of a rumble then truck sound... I think I went for about one year before I finally figured out what the noise was and for a while, I suspected the pulley. I even stopped at the dealer and the service rep came out and immediately said it may be an exhaust leak... I didn't believe him as it didn't have the truck sounds I was used to with classic GM rotted exhausts I grew up with in PA.

Read up here for entertainment: https://rennlist.com/forums/997-foru...lp-please.html

Peace
Bruce in Philly (now Atlanta)

Originally Posted by Bruce In Philly

That may be the water pump, but still could be air from a leak. Stepping on the exhaust should have no impact on the water pump... If stepping on the exhaust changes the sound, it is an exhaust leak... my bet.

Peace
Bruce in Philly (now Atlanta)

Here is what my failing water pump sounded like. This is confusing as the new water pump sounded quite similar but less loud and smoother. Also notice the alternator makes noise... that is the original from new now with 197K miles on it so that noise is, well, no problem. The water pump would chirp at startup, make odd noises at various times, and one day, I could smell something burning. But it never failed catastrophically and never weeped fluid. The .2 water pump is built for a battle tank IMO.

https://youtu.be/UvH9ahfrDnQ

Originally Posted by gdonn7

Even better video of the sound below, I’m ordering an X-pipe to pair with my PSE so when it’s time to install I’ll remove the left side to inspect:
https://imgur.com/a/Hn8AjOS

Originally Posted by Ericson38

I just had a very similar sound (left side) with my 2006 MT, 75K miles. Only at idle, blip the throttle to reduce it. Used a stethoscope with airbox off the car, engine at idle, carefully probing (be careful with it). Was the alternator in my case. Also changed the upper and lower idlers while there. The thing about turning on the AC is that it raises the RPM a few 100, and that masked my sound. Leaving the airbox on, probing around the alternator frame and you could still isolate it.