Yes, 4.1 is the latest OS. Your Nova has all the bells and the whistles then.

I doubt it is a bad knob. I'd even go as far as checking if its one of the analog inputs gone bad but then you would only get the noise on patches/multis that use analog inputs...

I'm still convinced that it is a power supply. The fact that you get more hum as you turn up some knobs is just another oddity caused by either an internal ground loop or possibly a bad interference that the power supply is picking up.

-ED-