[xlr8or]

Rodney if you look at the 1" cross bar that the rollbar support bolts go through you will be able to get some cardboard as mentioned between that and the panel.
Other option is to add rivets from the bulkhead side or dynamat type sound deadener in the trunk side.
Third option is that it's actually the trunk floor just behind the bulkhead. That rattled on mine as well. I took the diff access panel off from the trunk and put a 12X12 sheet of dynamat on the bottom of it. Cleared it right up.