Mbox mini crackling?

I recently purchased an older (probably 1st Gen) Mbox2 Mini. I am running ProTools 8 w/ it. Playback is crystal clear, but, after about a minute or so, it starts crackling and sounding very bad and grainy. If I go adjust my playback buffer settings, it seems to reset it. But, then it'll start doing it again after another 2 minutes. This problem KEEEPS coming back no matter how many times I reset, or shut the computer down, etc. It DOES NOT do this w/ my Digi003...never has once. Any help? Drivers I need to download? Anything?