Buzz from mouse in speaker

Hi!

I just registered here, because i am at my wits end, and hope someone has some insight. I have a buzzing sound in my speakers, which gets stronger when i move the mouse. 

My setup: 

Desktop computer - Mtrack Duo - Marantz 1530 stereo amplifier

The sound is a kind of high pitched buzzing static, which corresponds to activity on the computer, most notable mouse movement. I can also hear it at a low volume from the mobo itself, if i put my head in the computer with the speakers disconected.

It´s also transfered if i connect from the onboard motherboard audio card straight to the amp. I can however not hear it in a pair of headphones. Plugin into an active stage speaker greatly reduces the issue, to almost inaudible. 

Connecting another computer to the amp is trouble free. 

My best guess is that the source of the problem is coil whine from the motherboard. i have tried replacing the PSU to no effect. 

However i find it strange that the issue disapears when i connect to an active stage speaker. 

Does anyone have a sugestion for further troubleshooting or a solution?

Thanks in advance!