Before you waste hours and assuming you can lift that beast....take it to a friends house and see if it hums there. You either have a ground loop, something causing noise on the line, some transformer still plugged in near your amp causing interference...or you have an internal amp problem.
You've already eliminated the real easy things. Finding ground loops and noise sources can be very tedious....so first find out if your amp is OK.
You've already eliminated the real easy things. Finding ground loops and noise sources can be very tedious....so first find out if your amp is OK.