The best 40 mm fan which is available

I do not understand why some here he would think too loud. That he is not silent at full speed, you should see already using the technical data. 4,500 UPM can never be silent! From 3,500 rpm (with LNA, possibly two) but it is very quiet (much quieter than others in such a speed). If you still have a motherboard, which can control the fan even without PWM (which pretty much all day can), then you get him silently as he can turn down very far. That one with such low speeds with such a puny fan but barely transported air should also be clear.

One must also make no worries that he will soon loudly, because the camp no longer participates, namely what almost always happens in all (!) Other manufacturers. I have already determined by 12 different and they were all very early is no longer available because the camp was unbearably loud if it was not from the beginning. Only the camp of Noctua remain absolutely silent as the day.