once i put the car in neutral while driving the rattling goes away. it occurs once i've gotten up to around 3500, seems to be more aggressive in higher gears while driving even driving at 25-3k range. i think the car could have an exhaust leak at the manifold but i haven't checked. the car was in the ditch a few days back, just about a 90 degree angle with the road- front wheels in first, a pretty deep ditch couldnt get out by myself, so maybe the lowest part of the car '91 coupe, may have hit the ground and affected the manifold above. this rattling did NOT show up right after the ditch incident.

 

Well Jack it up and check your exhaust.