Sound Level Testing
While everyone "hears" noise differently there is one easy way to remove all subjectivness and easily compare different fans: use a sound level meter. This way you can easily compare the various fans noise envelopes without us coloring the results and see what fans fit within your personal comfort level. Of course, we will endeavor to try and explain the various results (which are taken at a 30 inch distance) to help you our readers get an even better understanding of how loud a cooler's stock fan is, but even if you discount our personal opinions, the fact remains numbers don't lie. All fans are tested with both voltage regulation / PWM turned off. 
From a noise point of view it appears that you are better off running THREE NF-P12-1300 fans rather than the stock two fans. If we were to hazard a guess why this is, it is because the odd match up of 120mm & 140mm does introduce some added resonance to the noise profile. Of course, a much simpler answer is that the P14-FLX is simply louder than the P12s. This would help explain why Noctua made it a full 100RPM slower than the P12. Our second guess is the more likely answer, as three P14-FLX’s was a lot louder than three P12s. All in all though, the noise envelope remains quite good.
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