Summary: I owned two of these prior and bought a few more to vent my cabinet. I combined it with a thermostat to turn off and on when the cabinet was on. My older fans were much louder and these are quiet enough that I no longer hear them even if they are on when there is not any noise in the house.
Summary: i've been wanting these fans for over a year but just didn't have the $50 lying around for these legendary austrian fans. i recently moved and said screw it and bought them since i had to undo my theater system anyways.
Summary: The price was right. For Noctua's that is. I bought 4 for 73.96 from Cool tech PC. I replaced 4 fans that came with my Cool@#master Cosmos case that were a couple years old. There was no difference in sound at all. Airflow dropped a little too as I cut down the rpm's.
Summary: This company is really remarkable. The packaging is luxurious and includes everything you would need to run full speed, low speed, molex or 3 pin. Of course you would expect nothing less from Noctua and their price tags, but still if you're looking to cool your pc case with something that will last...
Summary: I had some Enermax Magmas (great but just not quiet) in a server but switched to these for the noise. I've achieved the same temperatures without needing to use my fan controller to manually adjust the fan speed because I can trust that these fans do their job without hearing them.
Summary: The power supply fan makes way more noise, and it is a high end quiet power supply. The only issue is that the different resistor cables to control speed are not labeled. You need to go online to find out what the colors mean. Otherwise it would be 5/5
Summary: From what I can tell these are designed as case fans. Not as quiet as you'd think when they're have a grill or mesh in front of them, but at full speed that's to be expected. I am running them at half speed and they do their job at almost complete silence.