I spent ages trying to see if a fan had come loose etc but I think the pci e strain on my z170x gaming 5 board must be too much with 2x 3.0 x4 pci drives and a 3.0 x16 graphics card. All 3 are running at full speed. I was planning to build a new pc soon but wanted to wait until ice lake. I don't think I can live with this infuriating noise though.
The faster our rigs get, the more prone they are to coil whine. Proably not much you can do if you don't want to start exchanging components to find a way to get rid of it (starting with PSU probably), but there's no real guarantee there.
I press on each of the fans to check that they weren't vibrating due to being loose and that did nothing and did the same with the cpu fans which also did nothing but just not I unhooked the latches on the rear cpu fan and the noise quietened down ( although there is still a mild whining from the pc that I am sure wasn't there before ). And put some double sided tape on the rear fan and left the bottom hook off ( because the whining would start again with both on, even with tape ). So it may have been the cpu fan Hopefully that's the end of it. I really can't afford a full replacement and socket change right now if ot isn't.
Oh I misunderstood then, I thought it was some coil whine because of the added PCIe drive. Sorry, glad you found the source of the noise though.
I thought it was the drive too until I tried something different with the cpu fan after making this thread.