Some more information:
When I use the GPU (in games mostly), the noise is way louder! However, I tried removing the GPU but there is still interference in the monitors.
Could it be the PSU? I got a Fortron Hexa 500, maybe I need something better?
Also, when I plug the monitors to my MP3 player, there is no interference, but if I plug connect the player to the computer via USB, I can here interference.
Well, so, I think it either comes from the...