Why do those old bubble TVs make a high pitch sound?

Because they used a flyback transformer. Those were only found in cathode ray tube TVs; flat screen TVs don’t use them.

@thorninmud is correct, the old CRT monitors and tv’s ran the flyback tranformer at the horizontal scan rate of 15.734 kHz (NTSC, U.S. standard), which is a very high frequency note.

To answer your second question, I hear such sounds on all types of TVs including flat screens, but it sounds different and is less noticeable than the sound made by older televisions. For whatever reason, I am more sensitive than the average person to these high frequency noises, though, so most people probably can’t hear the noise of a flat screen. Most people don’t hear sounds made by old TVs either, in my experience. My family thinks I’m crazy because I can tell when a TV is on from across the house from this noise alone, but they can’t hear it when they’re in the same room.

@fly :: That is actually pretty common. In high school I stayed at a friends house a lot. His mom would complain about the tv when it was on mute and she was 30 feet away. Since we couldn’t watch tv at his place we went to the park and smoked weed.

@Fly if you hear annoying an annoying pitch out of a flat-screen TV it’s probably the switching power-supply (AC wall power to DC for all the electronics), or it’s the step-up circuit that makes the high-voltage (around 2–3,000V, not as high as for a CRT but enough to get your attention for sure) for the cold-cathode flourescent tubes used for backlighting most LCD sets (not the “LED” kind).
Higher quality sets will have silent power-supplies and silent step-up circuits, it requires a few more parts and higher quality parts so cheap sets will compromise there and elsewhere.

@dabbler Mine’s a cheap one so that might explain it.

@johnpowell Really? I’m surprised. Everyone I know makes fun of me for it and has no idea what I’m talking about. I know it’s not exactly rare but I didn’t think very many people can hear it so well.

Many put people, especially adults, lack the high-range hearing to notice that sound. Personally, I am less sensitive to pitches over 12KHz than I was a few years ago, and I effectively lost my hearing above 18Khz around my mid-20s. Of course, my hearing is still more sensitive to those sounds than the average person half my age.