Darn it!

My Mini's got this nagging "clanky" noise from center, underneath.
It sounds like a piece of sheet metal hitting on another piece of metal.

It only makes the noise going over a bump. Just had a new exhaust put on, so that was not the culprit.
Last time the Mini was at the shop, we mentioned it, and they tightened up some things, but the noise did not go away.
Any suggestions? It's driving me crazy!!!!!!