Review on case fan be quiet! Pure Wings 2 140mm PWM, black by Wiktor Winiewski ᠌

I bought a third blower from the front to the Fractal Design case, the rest are complete. Set to work in the range of 500-700 rpm. And while listening, I noticed that in silence we can distinguish a small rumbling sound that does not depend on the speed control mode (PWM - voltage), and it is this fan that makes it. Yes, the sound is heard only if you bring your ear close to the air intake. But I would like from be quiet! impeccability. So I'm taking off one star so they don't get arrogant.