If you are handy
I just bought a c320, no insulation, and it makes a fair amount of noise. anything louder than the wind is too much for me!So i plan to install insulation my slef. I've scoped things out, and I bought some 2" roll insulation from the local building center. This is fiberglass with an alum foil side (you don't need it but you get it as a package). I'm going to install it myself - some neat cutting, a little heavyduty spray adhesive, tape as required, and I will be good to go. Also going to check for cover vibration and install weather striping as required. Insulation ~$10, spary adhesive ~$5, razor knife ~$2, doing a job yourself, priceless. If you aren't handy, I recomend that you find someone to do it for you! you'll make a mess, be fustrated, and the noise reduction will be less than ideal. The other tips in this discussion are good too - don't cover the engine block or get to close to moving parts.Good luck!