I can tell you from experience that having a computer or other electronic device with a lot of fans inside can get very annoying. The fans generally produce enough of a hum that it sounds like a small jet airplane in the room. A new type of fan has debuted from RotoSub that promises to keep electronics cool and quiet at the same time.
The fans use active noise cancellation tech. Typically, any active-noise cancellation product requires a mic to hear the noise being made and then speakers to create the opposite wave to cancel the sound out. In the RotoSub fan design there is no microphone or speaker.
The fan blades are canted exactly to the right direction that they produce their own anti-sound wave to cancel the sound produced. All the person with a computer using these fans would hear is the sound of air moving through the fan.
via < ahref="http://www.gizmag.com/rotosub-noise-cancelling-fans/19463/">GizMag]