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Discussion Starter · #1 ·
Hey guys,

I have encountered a new high pitched whine/noise that seems to be coming from the dash or area in front of the instrument panel when I accelerate hard.

I first encountered this noise this morning while entering the freeway I was accelerating a little heavier than usual due to the location of this entry ramp has no accelration lane.

It started a whine/hum/noise and I was barely able to get it on video before it stopped. It is however repeatable, and tonight when the roads are empty i plan on taking a better video to get the sound better, because it appears that when I reproduced the sound for the video i was just at or slightly lower rev's than the required to make the sound because it intermittently whines where as when it first happend the whine was solid and continuous until i hit the brakes. This whine may be braking related, but it doesnt seem to be caused by them because the sound doesnt go away until the brake is applied.

Anyways here's the video, and sorry for flipping the camera around I expected the shot to show a wide angle of the dash not rotate the video as it did
 

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Discussion Starter · #3 ·
Well thats not cool. I wonder if it is indeed the alternator whether it has anything to do with the fact that my lights sometimes dim while the truck is idling, every 30 seconds or so as the truck sits and idles it will hit a rough spot and shake/stumble a bit and the lights go dim (this happens for about half a second then everything goes back to normal until it happens again 15-30 seconds later)
 

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It's probably the idler pulley bearing, or the tensioner pully bearing, remove the belt and turn the pulleys by hand, you'll soon find it.
 

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I had to replace my idler pulley on my old 2000 5.3L a couple of years ago for the same reason, started to squeal.

As to you lights dimming and engine stumbling when at idle, does your truck have electric cooling fan? or did you have defrost on to cause it to cycle the a/c compressor?
 

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You could have an electric problem, but you could also have a bearing that is so bad, that it is taking all of the engine's hp to turn the bearing, not leaving sufficient to turn the alt at idle under load.
 

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This just happened to me. Idler pulley drag and bearing or belt screech. The dimming lights is the clue. The idle speed is dropping too low due to drag on the pulley. My idler pulley was so bad it dragged the idle speed below the alt charge threshold at every stoplight. I could see the voltmeter dropping, and the lights would dim or pulse, It would only idle at about 400-500 rpm and killed 1 and a half brand new batteries. There was enough life left in battery #2 that once I replaced the idler pulley ($19.00) it charged up and stayed charged. I could almost not turn the old one with both hands. Also, if this is the issue, and the belt was screeching, replace the belt too. It has been really rubbing on that pulley.

The hardest part is getting the lock washer off the back side of the bolt. I had to flex the lock wings with a tiny flat blade screw driver before I could get it to thread off. I guess I will find out if that is re-usable, if the new pulley gets shot through my radiator.
 

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I have replaced everything with a pulley under my hood except the crank and the ac compressor. The ac tensioner pulley is located low in the engine compartment and gets exposed to water often. I have replaced that thing 3 times in the last few years. I have tried every company from ac delco to gates.
 

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That high squeal you hear is probably the belt sliding over one of the pulleys. The belt tensioner is a easy and cheap way to start. Don't forget to replace the belt, OR, your belt is worn out and it can't handle the heavy load. The lights dimming tell me that the belt is slowing down during and the alternator regulator is adjusting the output voltage to compensate for the slightly lower RPMs even if it is just a second or so. DANA W is right on his suggestions

A possibility is the A/C compressor is starting to seize up. I've had it happen a few times and you think there was a skinned cat under the hood. Was the A/C on of off in your video?
 
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