It's common for my wife to say as we approach a house, "the TV's on", when we may be 15 metres or more away, and the audio is inaudible.

The audio may be inaudible but the "raster pattern" - the 15,600-cycles-per-second sweep signal (something like 650 lines per frame, 24 frames per second) can be VERY loud, and easily heard out in the street through an open window, if the set isn't shielded somehow.

(I used to be able to do that too but then I got older and lost some of my high-frequency hearing. Sigh.)

And inexpensive dimmer switches often hum with a 60-cycle frequency, the way fluorescent lights do (though I think it's the ballast, not the bulb, that does the humming?)