Thanks for your response. We moved the media to another mac, and yes, when you play back through the deck, there are jumps in the picture, but the signal arrives on the tape just fine.
HOWEVER, the other machine actually had blocky picture breakup, like digital hits, during playback AND recording. So in the case of our first attempt, the picture played back with the recorded digital hits.
The same deck, cable, and source drive was used in both cases.
FCP v 5.0.4 was used in the first case, 5.1 in the second (working) case.
We also have Avid Xpress Pro 4.8 on the machine.
I’m thinking it may be some kind of QT interference, or a wonky FW controller. Unfortunately, the deck was a rental, so it will be a while before I can test it again.
Thanks for your response, and if you have any ideas, I’d love to hear them!