I have Audiobahn AS50Q 5 1/4" speakers in the rear and a pair of cheap 4" pioneer in the front(replacing them with 4" audiobahns tomorrow, along with new blaupunkt head unit), and Im getting alot of nasty distortion in the rear speakers when a song hits low bass notes, it sounds like something is loose or rattling around, but everything is tight as a drum, any suggestions?