I think that is the 19kHz pilot frequency for the audio signal that you were hearing. I used to be able to hear that as well when I was in elementary school. One can tell if whether the TV set is on or off without any signal/image.furrykef wrote:It doesn't really surprise me that I could hear 'em all. A while back we had this TV, and occasionally my stepfather or mother would accidentally turn off the cable box instead of the TV (the same button on the remote controls both). Since this resulted in a blank screen, they couldn't tell the difference. But I could always hear when it happened because it made a faint, high-pitched sound. (The screen also glowed a bit -- it wasn't pure black -- but I could still tell very easily without even looking at the screen.)
I loss that ability by the time I reached high school.