I done what Don told me to do, this is not an exact science, I tapped on different parts of the door and floor panels and the back wall both inside and out, if the panel seemed "live" meaning it had some resonance I put some CLD on it, usually just a small piece, I was actually having fun running around tapping on everything, I just used my finger to tap. This is the first step to reduce the "buzz" after that you want as large a continuous piece as you can with the mat, make as small a hole as you can when you have to and don't forget to shave the factory Styrofoam pieces in the bottom of the door so the panels go back on snug, about 1/4"