Thanks! I was looking maybe to use a bit less voltage to quiet it down, without too much of a performance hit/compromise.
You can simply put in a fan that has a lower RPM rating. I use for example a noisblocker in my APW3 and it is not possible to hear it. However the cooling ability is much smaller than the original Fan. This only works, since I use less power than the APW3 can supply.
Yes, that is an option too, but Noctua's fans usually come with Low Noise adapters (basically an in-wire resistor that lowers the voltage to 7V or 5V), so I was thinking maybe trying that one out and seeing if there's a noticable performance loss.