With your stereo upgrades, you'll probably notice a little bit of change. You'll find that you'll get less rattle when playing midbass in the doors, and it will sound a little tighter. The sound of the door closing will also change slightly because you are changing the resonant frequency with the mass of the Dyanmat. Dynamat basically adds mass to objects, and converts vibration to heat (so small you probably couldn't measure it). Before Dyanamt, guys used to use molding clay to add mass to doors. There are other types of damping material that spray on, and are designed to get into hard-to-reach areas like door panels. It's a small investment to try a small box of Dyanmat, so go for it. You can always add more in other areas or layer it up. I even used it on the underside of a stainless steel sink in my kitchen that would make a lot of noise when washing dishes. The dyanmat added mass to the underside and the pingy noise went away.
