My issues are growling when engine goes to V4. Goes away when back to V8. Thump in the rear of truck like spare is loose. Spare isn't loose. Are the springs binding and then unbinding? Transmission keeps shifting hard then slipping and when decelerating it upshifts. Dealer says onstar will detect but it hasn't and the issue remains. Interior noise from passenger side of vehicle. Dealer already replaced baffles. I test drove another like vehicle and the sound wasn't there. Left truck at dealer all day and nothing has changed. I noticed that other owners are experiencing similar issues. Can we get answers?