I dynamatted my entire trunk and still had rattle. One day I decide to find the culprit and I did...first you have to go to your local Home Depot and purchase a can of "Great Stuff" foam insulation make sure you get the blue can for windows. Next you'll remove all trunk mats and grey liners along the back and sides of your trunk to expose sheet metal...remove the black plastic piece that surrounds the trunk latch. Now on the trunk lid: remove the grey carpet piece to expose sheet metal. Now get your Great Stuff and spray anywhere you can get the long nozzle to fit...ideally you want to get in-between areas where metal meet metal. Spray inside the area where the rear lights are (there is lot's of gaps where metal will vibrate and resonate) make sure not to spray over the 3 bolts that hold the rear lights. Bumper: spray behind the bumper...the goal here is to fill in the area where the plastic bumper cover meets the metal bumper structure.

This worked for me and was able to get 95% satifaction