Try and hum along, maybe the TV is trying to jam with you

Take it to TV repair. I think it has nothing to do with it being an Android TV.

I know the Shield has a feature that can be turned on to play an ambient whooshing noise while there is no sound being played to prevent some speaker systems from going to sleep. Without more information it's hard to know.

Might be a grounding issue. I’d recommend unplugging the device and testing it in another room on a different outlet. If it occurs there then consult an electrician.

You have a grounding problem on the audio if you are using an amplifier or sound bar you should either try tightening or replacing the connecting cables otherwise you need to check the audio circuit on the tv board for loose connections or a bad solder joint