The sound levels recorded during these tests was near impossible to measure.
The sound of the pump was definitely now the loudest part of this cooling arrangement. So what I did was to use on the Enermax cooler at both stock while idling for the idle results. With the PWM IC in full charge of the fans speed, I really couldn't hear the fan operating and as the reading on the meter showed, 25 dB at this level is really great results.
Since the Enermax cooler was reaching eighty degrees I figured it was a much better test for the higher end of the PWM scale and with verification of the fans speed in AIDA64 I saw I was running at 1276 RPM and at this point I was hearing a slight whine from the fan, but still it was able to keep the level down to 45 dB at this end of the spectrum.
This is very impressive for a 120mm fan and it shows that Noctua even improved on their own numbers from previous fans they have designed thus far.