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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?
 

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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.
 

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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.
 

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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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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?
move got same issues, got lotsa ideas from lotsa friends. But still can’t find. I pulled all lower apart and it’s still there no loader no change. Have you had any luck locating the issue?...
 

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Just gotta love the guys that ask a question and never come back to read the answers, or report on what they found the problem to be. And in this thread with only 7 posts, there are 4 of them!
 
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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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Just gotta love the guys that ask a question and never come back to read the answers, or report on what they found the problem to be. And in this thread with only 7 posts, there are 4 of them!
With great power comes great responsibility.
 

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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?
Check those distributor take you a old piece of horse stuck one end to your district and one to your ear like astyhidcop
 

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……...I don't know, I'm not too keen on the idea of sticking an old piece of horse to my anything, ever...……...
 

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1999 GMC Suburban 7.4l K2500
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I have the same problem on my 1999 7.4l suburban. I removed the fan belt and it's definitely in the engine. Idles ok, Not sure if it's coming from cam. Maybe lifters.
 
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