[acjohnson55]

I also used to be able to hear CRTs. I didn't know what it was for a long time, and then I figured out I could "hear when the TV is on".

[EvanAnderson]

Oh, yeah. 15 kHz whine from NTSC CRTs did used to be a thing for me. Eventually I lost that range of my hearing.

A few years ago I fired-up a 15 kHz monitor for my Apple II and my then 5 y/o daughter held her ears and complained that there was a terrible screeching sound that hurt her ears. Between losing the top-end of my hearing with age and the end of CRTs being mainstream display technology I'd forgotten about tube whine.

[AStonesThrow]

The whine you hear is not actually from the tube itself, but generated by the flyback transformer.

https://en.wikipedia.org/wiki/Flyback_transformer