I've had (what I thought was) a ground loop problem with my gear: Macbook/Focusrite Saffire 6/2x KRK RP5s. There was a very high pitched squealing noise a few weeks ago; for some reason that went away when I moved the monitors but there is a low level hum on both all the time. I bought the ART Clean Box II to see if that would make it go away but it actually makes it exponentially worse. When I plug in the ART box I get a very loud buzzing/squealing noise that responds to processor load:
(If you listen to the clip beware: it's loud and ugly!)
Thats typical computer generated noise. They call it the noise floor. You hear it more when you move the mouse and thats called zipper noise. The Art will only help if you have a ground loop problem which you dont have.
The noise is usually very low level and only heard monitoring the sound and is not recorded to the tracks. Did you record the speakers to get that to tracks and amplify it up or was it really that loud to begin with?
That noise is normally well below the level you would be recording at. I use PCI cards to record and that sound is always there and nothing that will fix it. .
I would have to turn my monitors up to max for me to hear that much noise in my PC. I surely wouldnt be able to record or playback music with the gains cranked that hard, I'd wind up pinning my meters or blowing my monitors with that kind of gain.
Your tracks should be many many times louder than that background noise and you wouldnt be able to hear that noise at all during normal playback.
If it is that loud, I suspect you have a gain staging interface problem. Its the interfaces output amp that picks up the computer noise mostly. You shouldnt be hearing that noise on played back tracks.