If it is the cross-brace (kind of under the passenger seat) that the exhaust is rattling on, try either of these:
If you can loosen the exhaust, put a 1x4 in-between the brace and exhaust, then tighten the exhaust up again and remove the board.
If you can't loosen the exhaust, remove the cross brace and place a couple of washers on each bolt to lower the brace a bit, then put it back on.