Submaster weirdness

I've been experiencing some strange things with our submasters lately. At times, they seem to have a mind of their own. Examples :

When slowly moving the fader, the fader will 'catch' or 'grab' at points along the travel and take some force to continue the fade. This makes it a bit difficult to fade smoothly.

When faded down to 0%, the faders occasionally creep themselves back up to 1% for no reason I can see. They'll also bump themselves up a point occasionally when set to 50%. 

I'm also noticing discrepancies between channel level and submaster level. If I have a channel recorded to a sub at full, and the sub set to 50% (confirmed in the fader display), the channel readout will show anywhere from 49% to 51%. 

Related