Strange Engine Noise After Turning Off Engine - LISTEN!

[cutlassman]

Hi everyone.  A few months ago my 1992 Cutlass Supreme Convertible with the 3.1L engine started making a strange noise from the engine compartment after turning off the car.  It's gotten a bit worse.  There are no performance issues noted at all.  Car runs and drive like it usually does.  Initially I only heard the noise after turning the car off, but now I sometimes hear it with the car running.  Sounds like a hissing/moaning sound, but I cannot pinpoint the source.  Have any of you heard this and can you offer some advice?  I've had the car 16 years and this is a new one for me!

 

https://youtu.be/LPYlHC4f71E

[Psych0matt]

Fan bearing?

[Psych0matt]

Hmmm, I retract that thought after hearing the whole thing. Sounds like some kind of pump of sorts

[94 olds vert]

This happened to someone before if I recall correctly. Don't remember what the problem was.

[Imp558]

Mine did that, it was the evap solenoid cycling REALLY REALLY fast.

[Turbocharged400sbc]

the egr solenoids may still be cycling, unplug and retest to rule it out.

 

ive seen a few odd things caused by ground loop voltage drop/corrosion on certain circuits

[cutlassman]

Thanks for the suggestions.  I'm going to dig into them this weekend and see if I can take care of this.

[cutlassman]

I replaced the evap solenoid which helped my mpg, but didn't fix the noise. Also unplugged the EGR when hearing the buzzing noise and it's still there. Sounds like it may be coming from the brake booster. Any ideas? Sometimes I hear it when the car is running, sometimes just after I turn the car off for around 20 seconds. Sometimes I turn the car off and there's no noise. I've read about brake booster buzzing with some Toyota and Volvo cars, but not GM. I'm puzzled. The noise is coming from somewhere near the throttle body.

[jman093]

That's all happening with the engine off? Wow. I think you're on the right track with the booster. I'd start checking the booster/check valve, etc. Has to be a pretty good power source to make that much noise and the booster is gonna hold a lot of vacuum.

[55trucker]

If you suspect the booster isolate the booster & test to see if the problem disappears.

[Heartbeat1991]

If it's not the booster, I'd go with some sort of fuel system issue.  I've heard that happen with kinks or blockages in the return line.

[Padgett]

Sounds like a leaking valve on a vacuum reservoir. Did it happen while accelerating ?

[cutlassman]

Quick update: still no solution to this.  Must be vacuum related as it happens for about 15-20 seconds every time I turn the car off.  Rarely happens when the car is running.  No problems with idling, acceleration, or anything...just a strange noise when the car is turned off. I wish I could pinpoint the noise, but I can't.  If I come up with anything, I'll post to hopefully help others. 

[Imp558]

That really sounds like a solenoid cycling very quickly.

[cutlassman]

I swapped out the evap solenoid with no change.  Any other ones you can suggest?

[Imp558]

try unplugging it leaving unplugged the problem may not be the solenoid but the control for it

[mfewtrail]

Did you isolate the brake booster as suggested above? If not, try that. If you have a harbor freight store closeby, one of their $4-5 stethoscopes will make this very easy to locate.

[ron350]

Any updates on the loud noise?

[cutlassman]

Nothing yet, I'm just living with it.  Need to get a stethoscope and try to isolate the noise.  Seems it's coming from somewhere near/under the throttle body.  Sometimes I hear the noise as soon as I start the car from being cold, which is puzzling.  I changed the fuel pressure regulator a little over a year ago, so I don't think that's causing the problem...but I can't be sure.

[ron350]

About any 3 foot piece of rubber or vinyl tubing will work.

Just hold one end in a comfortable position in an ear and the other end to find the noise.

 

[cutlassman]

Just wanted to post a follow-up to this strange noise.  I'm still dealing with it and have traced it to what I believe is the AC Orifice Tube.  The AC system was swapped to 134A with a new compressor in 2015, along with a new evaporator and orifice tube.  The noise, which is some sort of a pressure release noise, seems to come from right where the orifice tube is in the line.  Since the AC cools fine, I'm not going to bother evacuating the system and replacing the part.  Strange, since the noise didn't show up until many months after the swap.