I'll be doing some work on my daily this weekend, weather permitting.

Finding and resolving a godawful noise is one of the top priorities.

When driving, the car will be normal for a long time. At some point, perhaps five or ten minutes in, it can but does not always develop a rhythmic chirp or whistle.

It has not always been in direct delta to rpm, but lately it has seemed to be.

​​​​​​Accessory belt is new this spring. Hub and idler
​​​pulley are new. AC tensioner and idler pully are new. Regular tensioner pully is used at this point but low miles. AC compressor is only 3 years old. Alternator is under one year old. Power steering is the only "old" pulley and it is an LS2 steel which has been on since 2016.

I don't feel it is the belt or pulleys. But I could be wrong.

The noise will start sometimes when the car is going up a hill. It will quiet down when going down a hill.

In my mind, it seems that if I keep low throttle inputs it won't come up at all, but that if I drive with some acceleration and shifting it is more likely to come up.

The video doesn't have th normal whistling / chirping. And part of that is because whenever I stop the car, by the time I get out with the hood popped the noise goes away back to normal. I've busted out the mechanic stethoscope to no avail.

But then when I shut the car off it trails off into the noise in the video. That definitely eliminates belts or pulleys.

Could this be coolant air bubble? I flushed the system and installed a new pump in May.

Could this be a failed or improperly routed catch can? I moved my MM gen3 from the nose to the passenger head.

This long pressure noise long after the engine has stopped moving has me baffled for the moment.

My first thought is the catch can routing.

What are your thoughts?

 

It seems to be more on the passenger side.

Another noise option may be power steering and air in the system?

 

My first thought from your description was belt or pully, but You have pretty much eliminated that. Then I watched the video. I agree with you 100% that it is NOT a belt or pully. I would say it is pretty clear that it is coming from a system that is pressurized (but thankfully not your brakes). That rather limits the possibilities. Test your AC, power steering, and vacuum lines. It could be the catch can. I wish I could be more help, but it's hard to say. Good luck. Let us know if you figure it out.

 

That would drive me crazy. It almost sound like a weird electrical interference (the trailing off sound)
Do you have the a/c on or off when it's doing this?

 

Ac can be on, off, mix door and settings changed... It does not affect the rpm related whistling nor the pressure release sound when shutting down.

For a short time I thought it might be an exhaust hole as it sounds similar to when the air tube on a header developed a crack. That would work with rpm. But so could pressure to the catch can, coolant, or power steering. Just buggers me that it fades out almost every time before I get to the engine. Even had a buddy stand by and I drove up to him but still evades us.

 

Sounds like the AC to me. Ive heard home units make kinda the same noise. Sounds like a high pressure sound.

 

Just a WAG, do you have any aftermarket electronic stuff? If yes, pull the fuse and see if it stops. That noise would drive me into more OCD derangement.

 

I tried chasing it on the way home again just now. Then I took it out again and still couldn't catch it. As soon as I park, the whistle goes away, and as I pop the hood and run around the door the sound from the original post here is gone. When my cell has battery again I'll post a noise of the whistling while driving.

Someone on FB had guessed at a bad brake master cylinder. That could be possible, though mine has no apparent leaks.

Yes. It is driving me batty. I like to keep the car near perfect. I just did a massive amount of maintenance and fixes in May when I had time in order to keep the car tight and happy for a long, long time. I'm guessing I am the culprit behind this. I just don't know what I did.

 

Moved to C5 Tech.

 

Does it sound like it’s coming from radio speakers? I can’t tell from video. If not vacuum leak of some sort. Check Pcv hoses check vacuum hose to brake booster. There might be others that are vacuum but I can’t remember without looking at car.

 

I’m no Corvette professional, but maybe it’s the hvac diaphragm. I believe the hose is near the battery, can disconnect it , cap it off and go ride around .

No noise , then hock it back up and find the bad diaphragm in the dash

Noise still there , we keep looking .