New Noise High Frequency Chirp with an Air Decompression Sound at Engine ShutOff

[viperBase1]

Hey Everybody,
25221

First off, The Orange Lure (LuLu :orange:) is running great.

Took her out for an early Sunday morning cruise n' was lucky enough to find some open/empty road for a few awesome pulls. :dude3:
Then went back to cruise mode...headed for the beach.
She was nice and warm and running SO smooth.

Started hearing this high frequency chirping sound, pulled over and popped the hood but could only barely hear it at idle. (engine still running very smooth).
Headed home for the garage.. chirping sound seemed to be getting worse.. but hard to tell..

In the garage at idle.. chirp was there but not that pronounced and hard to locate. Best guess is its come from somewhere behind or rear part of the engine.

Hit her with some Belt Dressing in case it was belt noise => no diff.. belt is fine.

Then turned the engine off and heard a decompression sound. PPFFttt-CHShhhhhhhhhhhhhhhh. Lasted maybe a 1/2 a second. Like an air tank decomp..

Under the hood, everything looks great. No leaks of any kind. Everything is super clean.

I let her cool down. Then fired her up again.. Engine sounds great, running smooth. Maybe could hear the chirp a tiny bit. Let her warm up again at idle.
Played with the A/C. Turned it ON.. worked fine.. no sounds.. Turned it OFF.. still nothing.
Engine is humming.. still running smooth and sounding awesome.

Turn OFF the engine and hear the decompression sound again. :confused:

Charging up the Droid phone now to see if there's anything on the OBDII.

LuLu is trying to tell me something..
Any help/input would be much appreciated.
Thanks!

[Steve M]

Get a vid of the sound...I've never heard anything quite like you describe, but it's hard to imagine with words alone.

If it is coming from the rear of the engine, maybe a pilot and/or throwout bearing going bad? Since the trans was rebuilt right before you got it, I'd assume those were replaced, so that might not be it, but there isn't too much I can think of at the back of the engine that would make noise.

[Hrysler]

Valve covers can build pressure. That's why some put on catch cans. They might be leaking at the back of the cover? Just a thought, there's not much else that I can think of than build air pressure. In the engine bay. Hope you find out what it is..

[viperBase1]

Get a vid of the sound...I've never heard anything quite like you describe, but it's hard to imagine with words alone.
If it is coming from the rear of the engine, maybe a pilot and/or throwout bearing going bad? Since the trans was rebuilt right before you got it, I'd assume those were replaced, so that might not be it, but there isn't too much I can think of at the back of the engine that would make noise.
On inspection (during the trans rebuild), the clutch n' bearing looked real good. Plenty of meat on 'em..prolly about 65%. So left 'em as they were.
I haven't heard (or felt) anything strange about the trans and/or clutch.


Hrysler
Valve covers can build pressure. That's why some put on catch cans. They might be leaking at the back of the cover? Just a thought, there's not much else that I can think of than build air pressure. In the engine bay. Hope you find out what it is..
(pm'd you)
After I read your post, thought about the new PCV valve I bought that was still sitting on the bench.
Swapped it in just cuz'. The old one was a bit gunky but still had plenty of motion in the floating ball valve. Maybe it got stuck in the closed position.

OBDII test was good. No Code Faults.
Double checked the PCV hoses and everything around 'em. All looked good.

Went to record the noise.
She fired right up (as usual..she's an F'ing Rock).
Still not a single dash light.
Cruised her around the hood to normal operating temp.
Took her out for a big gulp at Shell. She REALLY likes Shell 91. :t1509:
Rolled her out on the highway for a spell.

No noise or sounds.
Rolled back to the garage.. was carefully listening for the chirp..not there.
Turned the engine OFF..no air pressure decomp noise either.

Dunno. :confused:

LuLu needs new shoes. Maybe that's what she was trying to tell me.

If it happens again, I'll be sure to post a recording.
Thanks guys.


p.s.
Hey is there any chance the "air decompression sound" could come from the TPMS system?
I haven't researched the TPMS system at all yet..know nothing about it (yet).. just throwing it out there.

[Steve M]

Definitely wouldn't be the TPMS system.

Are you currently running a catch can?

[Hrysler]

It could be the pcv valve. My suggestion, take it for what it's worth, is just keep driving it. Look for oil leaks, more noise that can(easily)be diagnosed. If nothing shows its self than your good. If it is something serious you will know. I promise you..If not dont worry about it. This is a true fact, all cars make noise. It's like taking it to a mechanic. They want to know what it is doing..you tell them and they can't hear it or find it.. so now your out $200 and no answer.. lol.... Im saving you the hassle, just drive and keep an eye,ear on it. Sorry bud, that's all I have.:-)

[viperBase1]

No Catch Can. Those are illegal in CA.

[chicagopd50]

If u had the a/c on then I would look in that direction...

[viperBase1]

If u had the a/c on then I would look in that direction...
I would tend to agree with you.. AFAIK it's the only compressor in the system.
Initially, A/C was not ON.. Turned it ON & OFF as a test.

Thinking it over the last couple of days, the two big clues are:

A few hard pulls.. best ones so far.
Was warmest day for her so far


She got hotter than normal.

It is time for Transmission fluid flush and refill. Gonna take care of it this weekend.
This'll give me a look under the car.. will see what I can see.

[slowhatch]

No Catch Can. Those are illegal in CA.

Was everything re-installed and capped of properly after the removal of the catch can?

A chirp sounds like a bearing, maybe an idler pulley or any of the other accessory drive bearings? Does it change with rpm?

[Mopar'er no car]

Sounds like a chirp from the serp idler/tensioner. Get a new Serp belt and tensioner/idler if it's never been done. Even if it's not the problem your 10 year old beast needs it anyway and she will thank you..:):)

[Jack B]

Some possibilities:

1. The engine or valve covers cannot pressurize at idle, the drivers side engine vent would not allow this condition.

2. The clutch slave bearing only spins when the clutch is in or being released, rule it out. The pilot bearing is the same, it only rotates when the clutch is depressed.

3. The AC system also seems like a probable.

Does the chirp frequency change with rpm, if so, is it a one-to-one increase that follows rpm. You could look at the pulley ratio's up front to rule out or pin point the offender.

[viperBase1]

Was everything re-installed and capped of properly after the removal of the catch can?
A chirp sounds like a bearing, maybe an idler pulley or any of the other accessory drive bearings? Does it change with rpm?
Oh yea. PCV system is simple enough. I know I did it right. Capped off those ports for the ACR-X Catch Can setup and tapped both the ports on the front ends of the valve covers.
Pretty sure with new PCV valve.. nothing more to see or do with the PCV setup.

The only thing I hear with a change in RPM is the awesome exhaust note :dude3:. So maybe it goes away..maybe it doesn't.
If I can push her to reproduce the noise, I'll be sure to record it n' see what I can capture.


Sounds like a chirp from the serp idler/tensioner. Get a new Serp belt and tensioner/idler if it's never been done. Even if it's not the problem your 10 year old beast needs it anyway and she will thank you..
Yep. Slowhatch replaced the belt right before he released the car for close of the sale. Said he thought he heard it making some noise. Installed a shorter belt. (what a guy eh!)



Some possibilities:
1. The engine or valve covers cannot pressurize at idle, the drivers side engine vent would not allow this condition.
2. The clutch slave bearing only spins when the clutch is in or being released, rule it out. The pilot bearing is the same, it only rotates when the clutch is depressed.
3. The AC system also seems like a probable.
Does the chirp frequency change with rpm, if so, is it a one-to-one increase that follows rpm. You could look at the pulley ratio's up front to rule out or pin point the offender.

#1. Agreed. As long as the original PCV valve wasn't stuck closed. Doesn't seem like that was the case.
#2. Agreed n' good news. I'd expect to hear such noises sitting in the drivers seat.
#3. Agreed. Could be A/C system.

I'm liking the idea of replacing the Tensioner/Idler pulley. Seems like sound advice n' a reasonable thing to do.
Gonna get one ordered up and have it standing by.

Thank you kindly gentlemen.

[TrackAire]

I'm just going to throw this out there because I'm not 100% sure about the condition or operation of your PCV valve since I'm not clear of what exactly has been done to your car. If I'm understanding this correctly, the previous owner had a catch can installed. Is it possible that the PCV valve was modified or "gutted" in any way to help it work better with the catch can set up?

Another thought, can there be anything in the coolant system that is bleeding off pressure and making this noise (cap, hose, expansion tank, etc)?

Good luck finding what is going on...probably something very minor.

[viperBase1]

I'm just going to throw this out there because I'm not 100% sure about the condition or operation of your PCV valve since I'm not clear of what exactly has been done to your car. If I'm understanding this correctly, the previous owner had a catch can installed. Is it possible that the PCV valve was modified or "gutted" in any way to help it work better with the catch can set up?

Another thought, can there be anything in the coolant system that is bleeding off pressure and making this noise (cap, hose, expansion tank, etc)?

Good luck finding what is going on...probably something very minor.

The ACR-X Catch Can setup had its own taps on the valve covers. Nicely done too w/assistance from Morgan at VE. The stock ports & PCV valve were simply capped.
Nothing obscene was done to the original PCV valve. It was just capped. New PCV valve installed now..so that's over.

I don't think it was a coolant thing. The coolant temp gauge sits just shy of 200o and that's where it was that day.
Also if it were coolant, I'd expect to be able to smell it.. n' there was no such odor.

Yea pretty confident we'll track it down. Loving the fact that it's such a straight forward 'Murican engine setup. Not a big whoop.
Thanks man!

[Jack B]

Whether the pcv vslve is closed or not, the engine is an open vessel due to the pass side vent. Secondly, if the engine was exhaling, you would see massive oil residue in the air cleaner.


Oh yea. PCV system is simple enough. I know I did it right. Capped off those ports for the ACR-X Catch Can setup and tapped both the ports on the front ends of the valve covers.
Pretty sure with new PCV valve.. nothing more to see or do with the PCV setup.

The only thing I hear with a change in RPM is the awesome exhaust note :dude3:. So maybe it goes away..maybe it doesn't.
If I can push her to reproduce the noise, I'll be sure to record it n' see what I can capture.


Yep. Slowhatch replaced the belt right before he released the car for close of the sale. Said he thought he heard it making some noise. Installed a shorter belt. (what a guy eh!)


#1. Agreed. As long as the original PCV valve wasn't stuck closed. Doesn't seem like that was the case.
#2. Agreed n' good news. I'd expect to hear such noises sitting in the drivers seat.
#3. Agreed. Could be A/C system.

I'm liking the idea of replacing the Tensioner/Idler pulley. Seems like sound advice n' a reasonable thing to do.
Gonna get one ordered up and have it standing by.

Thank you kindly gentlemen.

[viperBase1]

Sounds like a chirp from the serp idler/tensioner. Get a new Serp belt and tensioner/idler if it's never been done.
Even if it's not the problem your 10 year old beast needs it anyway and she will thank you..:):)

^This^

19 months later :witless:... Times like this... make you say "perhaps I should've acted on that advice sooner".

The job was way too easy and was an $11 part. :slap:

Finally replaced the Idler Pulley and man what a diff!!
Noises from the front of the engine eliminated, easier starts and SMOOTH'r running operation.


Definitely gonna replace the Tensioner Pulley next ($6 for just the pulley / $82 for the complete tensioner on RockAuto).
Job looks to be as straight forward (just 1 bolt).. any advice would be appreciated and I promise not lag for 19 months!