Do TVs emit some sort of high frequency sound when they're turned on?

Ever since my parents got digital cable, my dad has a bad habit of
turning the cable box off but forgetting to turn the TV off. He can't
tell the TV is still on because with the cable off, the TV screen is
black and there's no audio coming from the speakers.

But I can always tell when the TV's on because I can hear some sort of
sound coming from it. My parents say they don't hear any sound coming
from it and think I must have Superman's ears.

I have no idea how to describe the sound. My guess is that it's
emitting a high frequency noise that my parents just can't hear. I
suppose it's similar to the sound a fluorescent light makes.

Any ideas what the sound is and why my parents can't hear it?


I once heard that there's a cellphone or ringtone that only people
under 30 can hear. It has something to do with the frequency. I don't
know if that's true but maybe that's why my parents can't hear the
sound the TV makes.