This issue has been driving me crazy for years now to the point where I was using only single monitor for the last half year. There is a crackling noise at idle and a much more pronounced noise when scrolling or doing certain other graphical tasks such as gaming.
I have KRK Rokit 6 G1 and G3 monitors along with Focusrite Scarlett 2i2 USB interface. The KRK Gen 1 doesnt have this issue but G3 does, I even replaced the G3 and it still has this issue so its not the monitor alone that is causing the issue. I did try swapping the balanced 6.35mm cables and power cables between G1 and G3 with no change so its not the cabling either. The issue persisted with both older and newer model of the 2i2 interface. Using different power socket may improve the issue somewhat but its still there. Using different USB ports on the PC makes no difference either. House is relatively new, built in the last 15 years so I would expect wiring to be ok.
If I plug the 2i2 USB port into an unplugged laptop issue is gone. What I do not understand is why isn't the audio interface eliminating noise? I mean the whole point of a DAC is to take audio processing outside of a noisy PC environment. What is the point of a DAC if it fails like this? I just don't get how noise could travel via USB port which is digital and survive ADC process. Is this just bad design of the 2i2 interface? What is causing the issue and what can I do to eliminate it? It really seems like the USB DAC is what should be eliminating the issue not causing it.