When you say bounce do you mean that it continues to bounce after you have gone over a bump? If so it sounds like your shock absorbers have given up. To make sure this is correct go the each corner and push down a few times to get the car to bounce - when you stop pushing down the car should stop bouncing - if it continues to go up and down then it is the shock absorbers at fault. Let me know what you find.
Mister D., May 2008