Digital Distortion On Playback

[howilostmyway]

I have a Yamaha MM6 Workstation, and I recorded a six-track piece onto the work station. I then entered protools, and recorded that song onto Protools. It plays the song during the recording, and it sounds fine, but then when I go to playback what has been recorded, I get occasional crunching staticky noises? Digital distortion? Most of the song sounds perfect but there are roughly four instances of a few seconds of horrible sound quality. Any ideas?

I have an M-Audio Fast Track USB interface...