I have an 84' Z28. Getting a strange sound whenever I accelerate or brake quickly. It's right in the center of the car too. The whole engine and exhaust was rebuilt right before I bought it but i'm having doubts on weather it was installed correcly. At first i thought it might be the drive shaft hitting the exhaust, but it's not constant, only when sudden forward or backward motion occurs. Any ideas on what else it could be?