Did you actually pull the plug out of the wall on the tv? TV's are "on" even though you turned it off.
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It sounds like it could be a ground loop hum. Is your TV hooked up to cable? If so, unplug the incoming cable line from the TV and see if the hum goes away. If it does, than you have a ground loop hum from the cable, which is not uncommon.
If no cable issues, than try lifting the ground on one piece of gear at a time until you find the guilty component.
Yes, I fixed a ground loop hum by doing exactly what jmcgrogan2 recommended. First make sure it's not your power plugs. If it's not, the cable may be it. I ran a separate ground cable to one of my cable splitters and that seemed to reduce the hum a lot. I've also had to run separate grounds to my tonearm and preamp in the past. I have a Rega TT which has a bad hum unless I have a dedicated ground run from the cartridge that I can ground. It's a very frustrating thing sometime. Start by making sure that all your plugs get power from only one outlet and go from there.