Dynamat is used by car stereo nuts to damp body resonance and stop the high frequencies from bouncing. Of course, glass is bad for this, but dynamat helps in other areas.
As a side effect it blocks road noise. You'll need to pull up the carpets and lay it down. Fitting the carpets again can be a headache, but MB carpets fit pretty well, and their molding is robust.
Some people also undercoat the car to deaden road noise, but I don't recommend it. Most of that tar stuff will end up trapping in some moisture and you'll get rusty floors down the road somewhere...
1998 C230 "Black Betty"