Ask HN: Do I really hear my CPU/GPU or am I getting crazy?

You are probably hearing "coil whine", where parts of the power supply circuits are vibrating and creating noise. If it only happens under very specific load, you can get the effect of only doing it while doing something specific. Displays also can make noise depending on what it is displayed, which probably is a similar mechanism.

Thank you very much!

Back in the 80s I could "hear" the CPU of my old 8 bit micro by turning the sound volume up to maximum. I assume that I was hearing some sort of interference, as that system also used to mess with nearby televisions.

You're not crazy, it's called "coil whine":

https://www.youtube.com/watch?v=HP73edpQwgc

No.

OK.

How do you know fans not running?

If it's the new Macbook, it doesn't have any fans.