We recommend that you calibrate your speaker's sensitivity so that you get a comfortable listening level when the volume knob is set between 1 and 2 o'clock. This will allow plenty of playback headroom and also allow you to use as many bits as possible from the output DACs when feeding signal to your loudspeakers.
If you are hearing white noise in your studio monitors at a low level with nothing playing - it is quite likely that you're monitors are not correctly gain staged with the +18dBu = 0dBFS output of iD22. So make sure they are set as illustrated above.