If you grew up before flat screens, you probably remember the strange whine or buzz that old TVs made when turned on. That sound wasn’t imaginary — and it came from something called a flyback transformer.

CRT (cathode ray tube) TVs used high-voltage components to fire electron beams at phosphor screens, creating images. The flyback transformer generated the necessary voltage — and in the process, it emitted a sound in the 15–16 kHz range.

Most adults can’t hear that frequency, but kids and teens often could, leading many to say “I can tell when the TV’s on even if it’s muted.” That eerie sensation? Pure science.

The buzz would fade as the TV warmed up. Today, the sound is rare — but nostalgia forums are full of people who still “hear it” in their memories.