EDIT: It was actually the Logitech G500 mouse emitting a high-pitched whine or squeal, not the motherboard. More information here: http://jdc.parodius.com/logitech/. I suggest contacting Logitech support if you're affected.
I have an Asus Gene Z motherboard which I'm using with a Logitech G500 USB mouse.
I have noticed an extremely annoying quiet but high-pitched squeal coming from the motherboard. I thought it was the fans at first, then the hard drives, and even thought it was an SSD at one point but it turns out it seems to be coming from the motherboard itself, somewhere around the I/O or PCI-E slots.
The noise is constant when the mouse is idle, but it stops when I start moving the mouse. I thought this was highly unusual and it seems that most other similar problems I've read about occur when the mouse IS being moved. Not in this case, however.
I have tried using a PS/2 adapter with the mouse but I don't think the G500 supports this as it needs USB. I have also tried with another mouse (G5). I have tried all my USB ports. I have also tried reducing the mouse polling rate from 1000 to 125 but nothing works.
Any suggestions, please? I have already RMA'd this board once, and I really can't be bothered disassembling and returning it again.