Clipping-ish noise? Help!

[Audiosprite]

I worked the bulk of the day on this duet mix, but when I listened to it on my Behritone, I started hearing this almost clipping-like noise pop up. It sounds like it's on the bass track, but if either track is soloed it goes away. You can hear it most prevelently from 0:20-1:00 and from 2:20-3:00.

http://dl.dropbox.com/u/3473417/kyledan 02 dan bari.mp3

I don't hear this sound on my monitors at all, but it's definitely on both my grotbox and headphones. None of the bus or plugin outputs are clipping.

 

[Audiosprite]

I spend two hours trying to work this out, all but give up and post a thread, then twist the Bass Rider Artifacts knob and find that's the problem. Nevermind. ಠ_ಠ

Still curious as to why both tracks needed to be enabled for this to trigger, and why I couldn't hear it on my monitors.