none of that stuff should hum brendan - no matter where it sits
there is a million ways to skin a humming cat but the best way is to unplug everything at the power point
and start checking with the speakers and amp first
if you get no hum plug the next thing in untill the humm shows up
leave that box off and unplugged
then add another thing back into the system
usually ground loops are to blame - not radiating fields err usually
basic stuff but hell i was chasing a mysterious humm an hour ago
it happens to the best of us
