My 06 LT is equipped with the Pioneer system and I was wondering if it is normal for the factory sub to rattle/buzz/vibrate at volumes higher than 40%? Could it be that the grille and/or the factory paneling in the hatch is loose? Or possibly that it is blown? The system still sounds full, it is just when you're in the back seat, the buzzing is prominent.

 

Check all the retaining pins to ensure they are tight

 

I had to put a piece of foam under the license plate. Something I learned from my stereo installer son.....