SilverStone PP02 Acoustic Cover
 

Direct Link: http://www.phoronix.com/vr.php?view=5380

Summary: "When one seeks to quiet their computer system while retaining
from eliminating any of their cooling components they often turn to
noise dampening products for their fans as well as turning down the fan
speed. One of the areas often overlooked by enthusiasts is the noise
emitted from the power supply. With us for this review, we have the
SilverStone PP02 Power Supply Acoustic Cover, which is a simple yet
unconventional product for silencing your system."