chirping on decel
 

hi everyone,

need help identifying a mystery sound...

80SC - i get a chirping sound when letting off the throttle (chirp, chirp, chirp... chirp). i thought it was my 3 broken head studs but i just had them all replaced (like a big storm cloud lifted from my shoulders). if it's bad alternator bearings the noise would be constant correct? only happens when i let off the throttle, doesn't matter what temp the engine is, does not happen at idle.

any advice on what to rule out and what to start investigating is appreciated

ap

When I read "chriping" I think of the tires spinning.. Is this what you mean?

At what RPMs do you hear the chirps?

it's definitely not tires. it does not occur when i accelerate, only when i let off throttle at any rpm until get to idle revs and it stops. like a little bird or rodent under my hood, or air/exhaust pressure being released through a small space.

i ripped out all the carpet and sound insulation so i can clearly hear it from the cabin, maybe i'll post a sound clip tonight.

This happens when slowing down in gear?

Could be the decel valve.....block it off and try again.

Also check belt/belt tension. Had a similar issue w/worn (slightly glazed) belt -- differential speeds between crank and fan pulleys led to small squeal on deceleration.

HTH

Are you running A/C? My A/C belt does this when A/C is on.

Loosen the oil cap and see if it still does it. I had to replace my restrictor in the breather hose, seems the vacuum from closed throttle would make the seal on the cap "chirp".

Never heard of the problem but the suggestion sounds plausible.......

Hey Andrew -- any update/resolution?

hi guys, sorry i was out of town til now...

andyt: yes only happens when slowing down in gear or between shifts, if i engage the clutch or put into neutral... nothing.

Joe Bob: do you mean by blocking off the connection at the back of the air boot? what would be your suggestion?

Flat Six: i replaced the belt about 4 months ago, tension seems ok.

Josh D: my AC hasn't worked in years so i've basically pulled out everything i come across AC related... i think.

DUK: interesting, i will try this.

here is a one minute video clip, chirps start at the 19 second mark:
Another mystery sound from my 911... on Vimeo

ap

The suggestion was to replace or clean the restrictor valve....

Any resolution to this? My 80 SC engine makes a chirping sound on decel, sounds like a wastegate popping off.

Do you hear it more or less at the front? I have the same thing going. I hear chirping a the dash area but its intermittent and not a common noise. Sometimes its there sometimes its not. I was thinking it could be from the AC blower or something.

This sounds like it'from the back. I found the gasket on my oil cap split. I am making a new one, will post how it works.

No difference. It's not a consistent sound, so it's hard to troubleshoot.

Does this model have an ambient air valve? If it does, I'd check it.....

My car makes this same noise, as heard in the video, on deceleration in gear. I just went for a drive and on long downhills in gear it was happening quite a bit.

Any tips from anyone whose been able to resolve this? I hate to bump ancient threads like this but this is the first one I’ve found with the exact symptom and a video, and there isn’t a resolution!

Hi Mike, first of all congratulations on your new car.

I still have the sound and yes I know how old this thread is LOL!

I don't think it's the head studs from all the posts I've read when you Google "what does a broken 911 head stud sound like", it really sounds more like an air/exhaust pressure type of thing, rather than a piece of metal slamming around type thing. I drive my car all the time, it run great and hasn't gotten worse. My mechanic says it's running great so just leave it but I'm going to a new shop for my next tune up and I can post what they say.

I believe I know the sound you are talking about. I've heard it a couple of times, both from cars that sat a lot. The chirping sound comes from the transaxle area and sounds like a metal on metal "cheap". On both cars that I had experience with the chirp was very reproducible and happened during acceleration instead of decal but it may be the same culprit. The noise was caused by movement in the drive train putting the transaxle in a bind with the mounts on one car and the clutch omega spring hitting the heat exchanger on the other. Same noise on both. Look for worn mounts and see if you can spot moving parts getting too close to one another. May be able to see movement by having someone rev the engine while on a lift.