Just helped a fellow VX'er with this today and turned out to be the right-hand exhaust rattling against the passenger side torsion bar. It only happened for him while stopped in gear, but the clearance is so close this could be the culprit for many of y'all as well. Replacing the main exhaust hanger may help as with time it stretches a bit, or perhaps putting a piece of phenolic half-tube around the torsion bar to give the exhaust something to rest against.