Recently bought a 2008 Colorado with less than 25,000 miles on it. I was told by the dealer (CarMax) that it had been in a minor accident and had suffered very minor damage. The truck runs very well except for lots of rattling sounds coming from the bed area. I also notice that the bed seems to shake when the truck is running on a bumpy road. None of this occurred when I first drove it but then it started about a week later after I found a small piece of 2x4 underneath it while parked in the driveway. Seems suspicious. Any ideas about what to look for under the bed which could have been braced with that piece of wood or related fixes? It's driving me crazy!!!! Please help????!!!!