I really wish I hadn't read this thread. I didn't notice it, but I read this, and mine does the same and now I cannot unhear it. I swear it getting louder, but then that's just my sensitivity to irritating noises.
So I now cannot unhear and I have a problem that I never knew I had.
This is the reason I don't put grey test screens up on my OLED TV, because I don't want to know about issues I don't know I have.
Dammit!
I managed to fix mine. I bought a Razer Core X and installed a Radeon RX Vega 64 and now I cannot even hear myself think, let alone any coil whine.
Simple.