Thread: Screeching Sound, But Not From Belt

2002 Pontiac Grand Prix 3100 SFI

Engine makes a high pitched screeching sound when engine is revved.
The sound is coming from the left side (front) of the motor, where the belt runs.
When driving, the screeching occurs when accelerating to highway speeds, or when climbing slight grades, there also seems to be a loss of power.
Backing off the throttle will stop screeching, and you'll be driving like granny.
I thought it was the belt, or a belt driven accessory like tensioner or water pump.
With the hood open I removed the belt and did a quick test. When I revved up the motor it still screeched... NOT GOOD!!!
It runs smooth and quiet until I accelerate hard or try climbing a moderate grade.
If I drive like granny there's no problem!
What internal parts could be causing this?


Also... I pulled and inspected the PCV... it's clean and working fine.
There is no excessive internal vacuum or back pressure.
If I punch the throttle I can get a quick screech (just like a belt would make).
If I slowly increase throttle, it will run smooth until about 3500-4000rpm before it starts to sound off... and all this happens with the belt off???

I had the same sounding issue. What happened to me was i torqued my intake manifold bolts too hard and cracked the intake runners ( prob not your case unless you did a LIM gasket recently) but i also noticed if i removed the oil cap, it would try to stall. when i got to the lower intake manifold gasket, the rubber was all chewed up and leaking air. Thats what i debunked as my squeal screech sound. Gaskets get damaged in these 3100 its all over the forums. Id say 90% its lame gasket, and decrease is performance?

Sorry, i didn't record the sound. But the issue can easy be found. By testing with the belt off eliminated the belted accessories. These engines are simple to understand with a little research. So the only thing left is the trans, air induction system, valve train, and crank/ pistons as likely culprits. i don't think it is the trans so how about the bearings associated with the crank? I could imagine those would be damaged from coolant getting into the oil. Have you been missing coolant or have coffee like oil? If so it would be your lower intake manifold leaking and alot of people would agree with me on that one. I think the valve system would be the least likely to squeek than it would knock like you said before. So the air runners are next. Air coming in from a filter and sensors going thu a TB are likley to whistle or squeelespecially if mods are involved. But what i think it is is the last gasket that fresh air goes by, the dreaded LIM gasket. The rubber between the head and the LIM in my case rotted away ( also cracked the metal there) letting the air screech through. I think you have a SMALL ( and getting worse) leak there which explains why at only certain loads you can hear it. And also makes it hard to pin point unless you take off your hood and drive while someone rides on your engine........ Ive seen it before haha.

Any progress on this issue?