Why is my Mac making a constant white noise

Loud Constant White Noise

I'm reposting this question because I finally found the answer:

This noise is hard to pin down. It goes away when put to sleep, but reappears when woken: same with shut down and restart. All apps are off and peripherals unplugged except ethernet.

If you are having the same issue I found the answer:

Its Google Chrome specifically some helper that seems to start in the late afternoon/morning in America. I use Firefox now and my PC is finally silent after years of driving me barmy. Hope this helps someone.