JDM-FREAK

after i dropped my car, it rattle on the rear side for some reason, itz not a lot, but itz annoying... i tried to find where it come from .. i just can't find it... can someone help me why is this happening?.. the sounds actually coming from rear-right, where muffler stands, and my car is 2000 and muffler doesn't touch the bumper at all either. please help~!!!!