i recently bought a marshall mg15fx and i use a zoom 505ii with it however theres alot of humming when i connect my guitar through the zoom. moreover is there anyway of switching from clean to distortion effects withous pressing the channel switch on the amp i.e through the zoom?
Just put your foot controller next to your zoom pedal. Although I'm guessing that's what your trying to avoid.

As for the humming. Try and locate where it's coming from. i.e. amp, power supply, leads etc. swap things in and out until you locate it.