Noctua NH-C12P CPU cooler Review
 

Once it was fitted it was practically silent in operation
without either the Low Noise Adapter or the Ultra Low Noise Adapter,
with those fitted I couldn’t hear the fan on the NH-C12P at all above
the other fans in my set up which isn’t at all noisy.

http://www.xtremecomputing.co.uk/review.php?id=441