Well, yes they do. That is why they are there to begin with. I noticed the transmission whine and rear diff noise, along with tire noise at speed were remarkably reduced. Conversation is easier at highway speeds (top up) and the radio/headunit sounds much better at a reduced volume. I stopped adding material forward of the seats because I thought I might go too far in NVH reduction and would not be able to hear the symphony that is the engine winding up.