Cooler Master Hyper N520 dual 92mm fan cooler
 

Heatsinks remain one of the primary noise sources in a PC, as they are usually equipped with a fan, and most fans make audible noise. While CPUs generally run much cooler than they did a few years ago, some still push beyond 100W, and high speed, noisy fans are still basic tools used by heatsink designers. SPCR's general recommendation for silent computing enthusiasts is to use a large heatsink with well spaced fins in conjunction with a large, quiet, slow speed fan which can move as much air as a smaller fan running at higher speed. The Hyper N520 varies a bit from this ideal in that it is equipped with two fans, and at 92mm diameter rather than 120mm, they are not as large as they could be, given the fairly large size of the heatsink. The proof, as always, is in the cooling.

http://www.silentpcreview.com/CoolerMaster_Hyper_N520