mine use to rattle really bad, first off the kenwood sub was blown and sounded absolutly terrible so i replaced it with an 8"kicker and it fit perfectly also sounds amazing. Secon i used to get really bad rattle it comes from the plastic that cover's the rear deck lid, i pulled the clips out and took it off of the metal and used some weather stripping to keep the plastic off of the metal. Second time i had a terrible buzz and it was the plastic covers were the cutouts for the 6x9 speaker wholes. hope it helps cause i know that buzz and rattle use to drive me nuts.
