ladies and gentle men, check your switch housings!
i pulled off both of the rear door panels and turned back on the stereo. even with the door panel off that damn plastic sheet still made a racket. so, as much as i know that those sheets are pretty important for keeping that little bit of rain that makes it through the glass seals off of the interior of the door panel, i took those sheets off of the rear doors. that alone pushed the vibration noises down a lot, but there was still a problem.
next i began to examine the door panel itself. i noticed a small white plastic box that was attached very loosely to the inside of the door panel. if i just hit the door panel with my hands i could hear it rattle. so, i decided that those needed to go too. here is what they looked like:
if any one knows what they are for the info would be greatly appreciated.
any way, i cut them out and that further reduced the noises i was hearing, but there was still a lot of noise coming from somewhere. turns out that those little silver pieces that hold the window switches were rattling like mad. so, i took them out and added a thin layer of soft self adhesive foam to the inside of the switch housings. then, BAM, no more rattling!
took all day, but i got it figured out. so, if you are having this same problem you may want to check those three spots.
hope that helps!