What is this noise???

[Dr.Zoom]

My gut says idler.

How old is the belt?

 

[chrispy]

I didn't notice any alignment issues with the belt during and after belt installation. I'll give a closer listen to those items mentioned tomorrow. I do know that while I was filming, it didn't seem like that pulley was wobbling as much as my eyes were seeing. Maybe camera focus or something. It's not a drastic wobble, but is noticeable.

I spun every pulley by hand while I had the belt off (minus crank), and all seemed smooth and quiet. Alternator had a faint squeak of higher pitch than I am looking for. When belt is on, I can put my ear right above the alternator, with and without screwdriver and the noise is not there. It's definitely more noticeable when listening with my ear directly above the throttle body area and from passenger side, so idler or tensioner are both good guesses. I just thought it might have been the crankshaft pulley, but my ears may have just been playing tricks on me since there is less engine noise from below, making it seem louder down there (maybe).

If I can't figure it out with the screw driver, I guess I'll start swapping out components one by one til I get it. I meant to try running it without the belt, but forgot until it was all back together again.

 

[chrispy]

My gut says idler.

How old is the belt?

Can't confirm age of belt. I've owned it for 7 months and haven't changed it myself. Looks to be in good condition, but I may as well replace it now to rule that out.

 

[chrispy]

The mystery continues....

Today I picked up new idler and tensioner pulleys, along with a new belt for good measure. Once I got the old belt off, I ran the engine without the belt and the noise was alive and well! So that eliminates pulleys and accessories.

I got it back together with the new parts and ran it for a while as I once again hunted for the source. I made a few observations that I'm hoping will be helpful in figuring this thing out.

1: I'm not sure if it's related, but is this normal? I am new to these trucks, and it seems odd to me that these bolts are backed out so far.

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2: What is this, and could it make the noise I am hearing? I put a screwdriver to it and listened from the other end, and I was able to hear the noise. So either that's it, or it's close to the source. (EDIT: Starter? but that wouldn't make noise while running would it?)

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3: I noticed the sound comes and goes when I rock the truck body side to side. Here is a video from below while I was rocking the cab. I had it in Reverse, since that makes the sound loudest.

https://www.youtube.com/watch?v=-dE2MZJO5po


4: Another video from below while I idle back in reverse and then brake, which also affects the sound. I go back and forth a couple times. You'll hear a squeak-squeak when I hit the brake to stop. I confirmed it is not suspension or brake squeak because I rolled to the same speed in neutral and there were no squeaks. It only does that when in gear (reverse).

https://www.youtube.com/watch?v=o1FI4_6BuuA

What do y'all think?

 

[sewlow]

Just a guess, but maybe the torque converter bolts are loose or maybe one or 2 have worked their way out? Gotta bit of a vibration when rolling?

 

[chrispy]

Just a guess, but maybe the torque converter bolts are loose or maybe one or 2 have worked their way out? Gotta bit of a vibration when rolling?

It's funny you mention vibration. I've been noticing stuff in the cab rattling more when I first start accelerating from a stop. I just thought my exhaust was getting louder or something. Haha. You might be in to something there...

 

[chrispy]

I am pleased to announce that I have found and eliminated the noise I question!!!

So I was under the truck pulling the cover to inspect the harmonic balancer bolts, and noticed when I put pressure on the motor/trans to break the cover bolts, I would hear a squeak. I grabbed somewhere on the motor and gave it a good shake and there was the noise!

Remember the pic I posted with the bolts sticking out of the bottom of the bellhousing? Well I was at the junkyard yesterday and found another gmc with a 4.3 like mine and found out the bolts are supposed to be holding two metal beams that bolt to the motor mount at the other end. For some reason they are missing on mine. So I pull the beams to take home and when I went to put them on today, they don't come close. And at the junkyard, the bolt that is fixed on the motor mount was on the driver side (passenger side was not fixed, so it could be removed). On mine, the fixed bolt was on the PASSENGER side, and the end was making contact with the frame! I'm thinking when the PO pulled the motor (he mentioned it was rebuilt at some point), the motor mounts were installed on the wrong sides.

All that being said, on a hunch I decided to bend the metal on the mount with a prybar just enough to get the end of the bolt off the frame. Noise eliminated. Crazy! Now I have a loud rattle from my cat converter (heat shield) to contend with.

Here is a pic of the bolt touching the frame.

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[sewlow]

Yay! Glad you found the prob!

 

[chrispy]

Does anyone know if running without those support beams will present issues in the future, or am I okay to leave it as is?