Why does your 1999 Volkswagen Jetta make a rattling noise when accelerating?

Take a close look at the catalytic converter shield. Also check your exhaust. It's held to the frame by two or three "rubber bands" that allow the exhaust to move with the car. After time, they break or become elongated and your exhaust can bang against the frame or the cat converter shield. The rubberbands are only a few bucks at the dealer and are easy to replace. Just make sure the tail pipe is not hot when you do it.