Clunk noise when slowing down...??

I noticed we are getting a clunk noise when slowing down for an off ramp. Makes the whole seat area vibrate with a very loud noise. Anyone know what this could be?

Check your exhaust piping. I had that experience once- turned out to be a rusted out and detached bracket "floating" on the tubing. If I slowed or accelerated quickly it would slide forward or backwards and hit.