you got your situation solved but it appears you have a problem with your electrical wiring...I would check or have an electrician check proper grounding of your fuse box...or you possibly have a loose ground in one or more of your electrical outlets...in any case it could cause other unwanted problems down the road.
sometimes just reversing the cord in the outlet will eliminate the hum...
In any case it is always wise to find the source of the problem and fix it or get it fixed.
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