I have tried some of the things that was suggested in this thread, nothing worked
- adjusting CPU frequency down and playing around with the core voltage.(this did change the volume/pitch of sound, but did not get rid of it)
- adjusting mouse DPI and refresh rate (no change)
- removed my GPU and used intel HD instead (no change)
- changing mac profile from IMAC 18.3 and to various MAC pro configs (no change)
I'm slowly becoming more desperate, and might try to order a better PSU which i have seen suggested on other sites... Right now i'm running a Corsair CX750M which is supposedly not the best PSU out there regarding coil whine.
For me it is always audible, and increases in pitch/volume whenever i start a program/move the mouse etc.. So it must be some kind of throttling thing, otherwise i would expect a more constant sound.
Also important to mention is that i'm running the system in an old MAC Pro cheesgrader case so there is plenty of room for the sound to get out of the case and absolutely no dampening.
Thank you to everyone contributing to this thread, i hope we will all find out what is wrong with out specific system.
Keep hacking ya'all