Try turning off your pc monitor, the photons spilling out of the screen will cause interference through the pickups. Also, make sure that any audio cables are not crossing power cables and that your amp is not too close to a large power supply (eg extension plugs with power convertors etc). Try setting up the amp and gear as far from the pc as possible and sitting as far away from both as you can. Hum on the amp can be reduced through phase invertion in your software package (if it can't be reduced by any other means). Hope this helps.