New Ground Loop - What Could Have Caused?

If the above doesn't help, check to see if there were any storms in your are that could have caused damage to your equipment (if left plugged in) or something else from a nearby lightning strike. Also ask neighbors if they had anything strange happen (electrical) while gone. This would be a possibility if disconnecting the cable doesn't eliminate the hum.

This sounds like the neutral wire that is also tied to the ground was no longer making a good connection. The bad connection could have been in your main breaker panel, meter box, or utility line feeding it. Without this connection, your outlets could have 240 volts coming from some of your 120 volt outlets, down to zero volts from the other outlets, do to a bad neutral connection. A lot of the time, anything that draws a low amount of watts, will usually get the higher voltage, and burn out. That neutral wire keeps one phase (hot) line at 120 volts, and also the the other phase (hot) line at a 120 volts, each half of the 240 volt line. It's good to hear everything is fixed, and no major loss.