Aah, yes, I remember the gravel in the hubcaps and potato in the tailpipe, and while it was easy to spot, a 12" length of bicycle inner tube slipped over the end of the tailpipe made some unusual sounds, too.
Does anyone still make the fireworks that had wires you attached to a ground and a spark plug? When the car was started, a long whistle, explosion, and smoke. The first time I saw that one was when Dad put one on Mother's car. She failed to see the humor in it./w3tcompact/icons/laugh.gif