I recently bought a 2003 Tahoe LT with 125k miles. The truck is real clean and well taken care of, but recently it started making a random noise it doesn't happen all the time and when it does happen it usually makes 1 or 2 popping/hitting sounds and it only happens when I'm driving forward usually faster than 30 mph. It sounds like something popping up and hitting the floor board near the rear. I have had the u joints and they seem to be in good shape. I also looked at the exhaust and everything seems to be normal here also. The noise travels so to me it seem like its coming from the rear. Does anyone have any ideas or guesses as to what this could be?