Can you figure out where you are hearing the rattle coming to the inside of the car. Is it like something hitting or rubbing the floor? or driveshaft? or where the rear springs mount to the uni-body?
Have you had the time to jack up the car and push, pull, pry, bang, pound, whatever else you can think of with different methods to try and get the same sound pinpointed to its source?
I deleted your other post that was essentially a copy of this one, as you had went back and edited it, it almost matched this one word-for-word.