I've been considering drastic measures to cut the noise down from my PC, hopefully completely. It is very annoying - I sleep in the same small room as it. On searching for sound insulated cases, I came across seemingly the ultimate, and certainly one of the most expensive, pre-built commercially available cases. A review is here http://www.ocprices.com/index.php?rev_i ... on=reviews
What very much interests me is the innovative and unique "whisper box" available that sticks onto the back. As the reviewer says, I imagine the bulk of noise coming out of an insulated case comes out of the unpadded rear. This seemingly solves the problem.