I've been getting an intermittent buzz/vibration from the engine compartment for a bit - finally figured out that the cause is the serpentine belt visibly vibrating and shaking perpendicular to the long straight run on the driver's side of the engine. It will vibrate until it hits a certain frequency, buzz/vibrate for a few seconds, then smooth out and start the cycle over again. This happens with the A/C on or off, but the effect is much like the compressor cycling and loading/unloading. The belt is a Gatorback, has less than 3K on it, no signs of misalignment or deterioration. However, I can press the belt on this straight run with two fingers, and get about a half inch of deflection and movement of the tensioner - does this sound like a weak tensioner, or should I be looking at another cause? TIA -

 

Does it only do it when cold? I was locking the gates at the shop the other day and noticed a strange noise coming from under the hooed of the truck but I could only hear it if I was standing in front of the truck. I pulled the hood and couldnt see anything wrong. Reved it up a little bit and the noise went away. I thought it was the fan clutch making a little noise because it gradually went away as I kept the rpms up.

 

I'm not sure. Several threads on here and over on TDR for those of us with shredded belts on 04s and 05s, but most of us were not diagnosed with any issues - i.e. - tensioners or pulley problems.

Why did you switch to the Gatorback? If the belt seems OK, it probably wouldn't hurt to replace the tensioner as a precaution.

I don't trust the belts on these things as far as I could throw the truck.

 

Sounds like the noise may be "keeping time" with the preheaters cycling, on their post heat cycle. When a preheater is on it draws over 100 amps, and the alternator works pretty hard to keep up. That is probably the movement you are seeing in the belt. Watch your underhood light, or headlights, and see if they dim when the belt fluctuation starts.

 

I work at Gates and if you need a belt I can get you one.

 

My truck was making a funny sound. The best I can described it is it sounded like a hollow sound,, like in a coffee can. You could really here it best if you put your ear right in front of the radiator. Turned out to be the tensioner.