I have what seems to be a tinny rattle comming from my 1997 Cruiser. Sounds like bb's in a tin can but it only can be heard when drivetrain is cold after a while driving the sound completely goes away. You cannot hear it at idle or revving the engine, only when you drive at low rpms. i think there is a rock stuck in the cat sheilds but?? Anyone have any idea. The truck has 41K on the clock and its like new. Never towed with it never beat on it at all. This noise is driving me nuts!! Help!