I wondered about that, I remember when I was a kid and we still had a tube tv, I could always tell if it was turned on, even if the screen was black or I was behind it in the other room because I could hear that high pitched frequency. It's also nice to know I can still hear high pitched frequencies even now, given I could just barely hear that high pitched morse code at the end, even if I couldn't understand it due to not knowing morse code, and I'm in my mid 30s now.