A weird sound just popped up I need your help with. See the YouTube below as I could not upload.
It only happens after the car is warmed up.
It does not vary in pitch or volume with increasing RPM
Comes from rear
After turning off the car, and turning the key back on, it makes sound for. few seconds and sounds like it it running out of "air"
For those above a certain age, when the car is running, sounds like ringing ears!
The fact that it stops when I turn off the car, but they start back again for a few seconds when just turning the accessory on is making me thing it is not mechanical but I have no clue.
Any thoughts?
Sounds like something in the vacuum system. If this is a
987.1
the obvious guess would be the
AOS
. If not that maybe something with the
brake booster
vacuum pump.
This is a
987.2
and I was thinking the
AOS
as well. The fact that it stops when I turn the car off, then it returns for a few seconds when I turn the key to accessory seems to rule that out. Maybe I'm wrong.
Your car is haunted. I will take it off your hands if you like!
It is of course really hard to evaluate a cellphone recording. Please troubleshoot by getting a mechanics stethescope. Because the sound is reproducable, you should be able to narrow down the source. Pull the top engine cover and/or work from the underside of the car. You are right, since if remains with the engine off, the sources are reduced dramatically. I'd think systems that are designed to run with the engine off and on. The engine compartment fan comes to mind. The supplemental air pump is another. Also the
fuel pump
.
The vacuum source for the
AOS
is the natural vacuum (depression) in the intake manifold. If the engine isn't running, there is no vacuum. The vacuum pump mounted on the end of the drivers side cylinder head is only to supply vacuum for the braking system. It only works when the engine is running.
I do not recall the
Cayman
having a vacuum reservoir tank but you might google that. Most cars, for safety reasons, provide some measure to keep vacuum power assisted brakes operational for a short period after the engine is turned off. But I am not familiar how this works on a
987.2
.
I missed that part. You're right, I don't think the
AOS
would see any vacuum when you did that.
Definitely haunted. Check your trunk (not the frunk) for Halloween ghouls. Sounds like someone is shrieking!
My vote here is vacuum -- given the timing of the sound and the pressure once the engine is turned off. Having just done a bunch of
exhaust
stuff on my
987.2
, I have not found any vacuum canister (reserve) or the like. Assuming your car's
exhaust
is stock, there could be a vacuum leak involving one the hoses, especially if you have
PSE
(do you have
PSE
?).
What I would do
next
is to find where the sound is coming from -- specifically. That means, especially as the sound continues with the engine OFF but accessory position ON, is to jack up the rear of the car and potentially get under it (WARNING - NOT WITH THE CAR RUNNING) and determine where the sound is. I would not be surprised if it is on the rear driver's (left/port) side. If it is, I'd remove the rear skid plate and do it again. If not, then I'd go into the engine bay to hear for the sound. YMMV and let us know how you get on with it.
Not sure if this helps, but have you noticed any changes in fuel consumption or performance along with this noise? Sometimes these things can be related. Just trying to think of any possible connections here.
Bet you find the source of the noise in the vapor recovery system. Sounds like some component that was under vacuum bleeding down to air. Or the brakes - does the brake pedal get hard after that noise happens? The reserve for the
brake booster
is the
booster
itself. There could be a leak that closes up when vacuum is applied to the system, but when vacuum is off - it starts leaking down - making that nice whistling sort of noise.
