During normal running, it's as quiet as any geared hub-motor, but if you go too slow in high gear, the commutation pulses induce a juddering noise. The same in low gear. If you try and go up a very steep hill without pedalling, the motor slows right down and then can make a rasping noise like something is resonating with the commutation pulses. Extra grease helps a lot. I think it needs a sine-wave controller. Xiongda said that one was coming soon a couple of months ago.