do you have a hatch or coupe?
-if it's a hatch, try stuffing the third brake light on the spoiler cause it stopped my rattling.
-if it's a coupe, did you replace your rear speakers or take off the rear deck at anytime? usually those cheap plastic tabs don't absorb enough of the vibrations and the rear deck ends up flopping back and forth.
-one other thing, where ever there are bolts or nuts holding in something to the chasis, unscrew them and place some type of dynamat to both sides. :thumbup: