I picked up a few Eloops to play with.. they are the 400-1500rpm PWM version. I have to say they have some pretty bad noise at 1000 rpm in my case.. I run them around 600 normally and they are very very quiet but during games they ramp up a bit and at 1000rpm there is a pulsing resonating noise. I found if I hold a little pressure on back of the motor the noise goes away. I can't believe how much vibration is felt touching the back of the motor on these things and still feeds through to the case despite its mounting system. Not as impressed as I thought I would be. If that noise was not there they would be awesome.

Yeah, I noticed that too, although only with the fan mounted on my Kuhler 620 radiator, oddly, not with it mounted on the Ninja. I blame the material that the blades are made of, it feels brittle and makes a very strange noise if you tap it with your fingernail.