well if you can actually turn the volume up and down and the clicks get louder or quieter... I'd lean more towards it could be something coming from windows that's causing it. Possibly a bad driver for the sound or something running that's making the sound. Try a diffrent set of speakers/headphones, see if they do the same thing. If they do, then it's most likely coming from the computer, not the speakers. And vice versa.

Do you hear the sound if you have something else making sound, like a song or a video?