This is my home computer. It is noisy due to the fan, harddisk vibration. I managed to find a quarter piece of sound mat for soundproofing of my car. As it is only a small piece left, I intend to test it on my home PC. My home computer is always noisy when the harddisk or fan spin causing the chassis to vibrate.

Here's the picture of the sound mat (Clasani Sound Mat). The effect is fantastic. My computer is now less noisy as the chassis vibrate lesser.