Yes, the back wall flex is crazy. I had no deadener, but all trim panels on and the back wall still jumped out 2 inches or so when i played some decaf. IDK how hard it is to remove the headliner though. Should've pulled mine out and deadened it before i started my wall build, but I couldn't afford deadener at the time and now I cant get the headliner off... Oh well, Ill take a dremel to it if its too bad and atleast be able to deaden the front half.