I’m curious, how many people are aware of these sounds. I have designed, etched, and built my own switching power supplies along with winding my own transformers. I am aware of the source of the noise. So, does anyone else hear these high frequency sounds regularly?
I don’t think I own anything that makes noise like that anymore, but we used to have a big TV a few years ago that I could tell was on or off from the other side of the wall.
E: I just remembered that my speakers sometimes make noise if I listen at a certain angle and last week I heard someone’s iPhone charger make a ringing noise while sitting on the socket so I disconnected it.