Can anyone help me with this sound? Happens as soon as I turn the car off. I have AC and usually run it but this morning I didn't for the purpose of this video. Makes a whine noise that fades out into a hissing sound then it's gone. Sounds like it's coming from the rear of the intake area.

 

I would've guessed ac. I would get a stethoscope and see if I can pinpoint the area.

 

LOL thats crazy never heard something like that

 

Could be a vacuum leak. The vacuum reservoir is supposed to retain vacuum beyond the check valve, but if something is leaking that might be the result.

 

Discovered I have just shy of 90 psi in cylinder 4 during compression test. Haven't found what that noise was, but wondering if this could be a cause? I'll plug off all vacuum at the intake to bypass the HVAC and what not, see if that is it.

 

Sounds like normal equilization of the a/c system to me, but I couldn't watch the video. My Express van squeals, hisses and you can hear the liquid refrigerant boiling out of the evaporator for a good minute after you shut it off.

 

Just wanted to update. I have since swapped to a vortec 350 with stealth ram and don't hear this anymore. When I tore the engine down, almost half the pistons had broken ring lands. That may have had something to do with it.