VERY High Pitched whistle/squeal/scream coming from motor

Discussion in 'GM Powertrain' started by djturnz, Jan 3, 2012.

  1. djturnz

    djturnz Member

    At idle my wife's 93 Suburban (350) has developed this high pitched whistle. I cannot locate the source.
    While accellerating it goes away. While coasting it comes back. If I feather the gas I can change the pitch slightly. Originally I was thinking the IAC valve was the culprit since it was only doing it at idle and near idle RPMs.

    I took it to AUTOZONE and found a Chevy guy there. Originally I was going to just buy the IAC, but I decided to ask for another opinion. His opinion was that the IAC would make more of a sucking sound than a whistle because air is goig in, not out. I agreed. He thought it was the alternator, so I removed the alternator and the belt. Started the truck and the sound was still there, no change.

    It's very hard to pinpoint because it's so loud. It actually makes me start to feel sick in the stomach when I try to listen too long while I poke around. I also want my neighbors to like me and therefore can't just let it squeal out front for 20 minutes while I poke around.

    We also tried spraying starter fluid all around figuring it would stumble if there was a vacuum leak. Not even a sputter.

    Also, it idles perfectly.

    I put it all back together in the parking lot (yeah, I was THAT GUY) in the rain. One last parting suggestion from the parts guy was that the bearings in the distributor were going out. Don't know about that one.

    Any thoughts?
  2. 95RedBarn

    95RedBarn New Member

    Im having the exact same problem right now and cant figure it out either....did you happen to get anywhere with it yet?
  3. Jaele

    Jaele Rockstar 100 Posts

    I would almost put money on the IAC. Take it off and give it a good cleaning, let dry and put it back on.

    Another item to check would be the tension pulley for your belt. But I'm still leaning to the IAC.
  4. BigMattKC13

    BigMattKC13 New Member

    Did anybody figure out the problem for sure. I'm having the same issue on my '94 Silverado (350 engine from a 96 Suburban). I was thinking the IAC but it idles perfectly. I also noticed it's much louder on the drive side.
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Usually a high pitched scream that changes as the engine speed changes is a bearing that is being turned by one of the belts under the hood.

    Usually, it is the idler pulley bearing, or the tensioner pulley bearing.

    You'll need to remove the belt and turn the pulley(s) by hand. Very tight, very loose, will cause the noise.

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