When I drag a really big layer in Photoshop a high pitch sound comes from my Macbook. When I stop dragging the layer, it stops. I have SSD and you can clearly hear that sound when there is no fans running. Is it possible to hear your CPU/GPU?
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.
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":<p><a href="https://www.youtube.com/watch?v=HP73edpQwgc" rel="nofollow">https://www.youtube.com/watch?v=HP73edpQwgc</a>