This is a fairly common issue in the PC world.
Ensure that you don't have an audio input or microphone enabled as these can introduce noise.
I don't know what type of KRK speakers you have but if they have a digital input you could use that to eliminate the noise. I had the same issue then switched to the optical output to my receiver and the noise issue was gone.
Short of that, unfortunately, there is no, good/easy fix.
With a nice set of speakers like those, I would recommend you get a sound card which could eliminate the issue.