"First thing I decided to do was install some sound dampening material. I looked for the best deal, and came up with some Sonex sound foam from 2CoolTek. $9 for a panel of the material. After receiving the it a few days later, I had to cut each piece to fit the side panels. It's easy to cut with scissors or a simple serrated knife. I used some 3M spray adhesive (really cool stuff if you've never used it before) to attach one section of Sonex to the panel opposite the motherboard, and the other panel was able to sit in place in-between the panel and the rest of the case.. if you catch my drift. I used the remaining piece that was cut off from the panel section for the top of the case, which was also able to rest in place without any adhesive. With the remaining material I was able to fill my empty drive bay covers. "
FULL STORY @ VIRTUAL-UNDERGROUND. (http://www.virtual-underground.com/articles/QuietPC/)