Dynamat is a sound insulation material. It is sold on a roll. If you want to go this route, just stick it underneath the carpeting or wherever you want to add more sound insulation. It is a good material, however, it is a bit pricey.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record