Sound cuts in and out

I am running Mainstage 3.0.3 on my MacBook Pro - 13" (early 2011), OS X 10.9.1, 2.3 GHz Intel Core i5 processor, 8GB RAM and running on a Samsung 500GB SSD drive. I am plugging in a bass through an M-Audio USB Fast Track.

Using this right now simply to play along with tracks on iTunes (for practice). Used to use Garageband for this, but then I got Mainstage. Mainstage 3 was running fine when I first bought and downloaded it. Not sure what the problem is now, but when I open it and create a new concert (bass-rig) then turn the master volume up, the slider movement is choppy and the sound/signal cuts in and out (more out than in). The only time I can get sound to consistantly come out is if I click on a menu option, like File or Edit or Action, etc... if I click off the menu, the sound cuts back out and I get nothing.

Sound works perfectly fine through Garageband with the same setup.