I have a 2006 Silverado 2500 4x4. I am hearing this bang noise (sort of like a hammer hitting the muffler) periodically when the truck is warm. I am hearing this "bang" noise when the car is cooling off after a drive and when the car is idleing like in a drive thru or at a signal. It seems to happen every 30 seconds or so but it is starting to really bug me now. It sounds like something hitting a tin can but it is fairly loud. Does anyone know what this might be?