Chevy Colorado Noise

I recently bought a 2004 Crew Cab 5 cylinder Colorado. I really like the truck alot. However; since the first day I owned it I noticed that when accelerating and the Tach hits 2000 there is this odd whinning/ vibration noise. Its alway happens on acceleration and at a very specific point. If the tach is a little above or below 2 the whinning/vibration noice is not present. In city driving it is especially noticble with all the stopping and starting. I have even had a few people ask what that sound was. I have an appt on Tuesday with the dealership, but I was hoping maybe someone else had this problem and could shed some light on the problem. Then maybe I could send the dealership looking in the right direction.

I used to work at a Chevy dealer, and we saw some similar problems on full-size trucks. We found an unusual exhaust pipe vibration. It's a GM...anything is possible.

I had the exact same problem with my Colorado. Took it to the dealer and it was the exhaust heat shield vibrating. They adjusted it and it is a lot better now. Can still hear it sometimes, but better than before. There is bulletin out on it.