random audio playback

We're having some major problems with audio sync on the timeline. Video is captured 8-bit Uncompressed via SDI through the AJA IO. Audio is captured at a seperate time from a seperate source, analog, from a Betacam tape with synced timecode (everything synced from a timecode generator at the time of recording). Lay video down on the timeline, lay audio down, match the timecodes, and woila! everything looks great.

The problem is, at random times during timeline playback, the audio will no longer play back from the point where it should be playing back from. It will skip to some other part of the audio clip and play back from there instead. Say we transition into a section of the timeline where we are beginning a song (a spot which has played back fine for all of the previous editing that has been done), but now the video is correct and the audio begins that clip mid-song, even though the timecode still matches. The editor is having to delete the audio from the timeline and lay it back down to fix it.

This problem is extending itself into quicktime movies rendered out from the timeline - the real problem. The timeline might play back fine, but then when we render out a quicktime, all of these sync errors pop up.

We've tried trashing prefs and doing the "audio mixdown magic", to no avail. Anyone have any ideas?? Any help would be much appreciated.

Nick