Could be the cord. That can be difficult to diagnose. Purhaps it isn't firmly connected. Move the cable around in the middle a little to see if you increase the problem.
Could be the camera. Watch the camera window. Retry that footage too. I like to rewind my tapes from the end to the beginning in an attempt to loosen it up a little.
Could be your computer. Perhaps you have some other demanding applications open, or your sharing a drive with other users, or your importing to a firewire drive on the same firewire bus as the camera, or your drive is fragmented, etc. Close down all of your other applications.
Simply put, it is difficult to figure these things out. When I've had this problem recently, it was because the recorded image sucked. I had copied the content from a VHS source to my camera (doesn't have pass through) and then connected that to the Mac for import. Even original camera recordings occasionally show that problem. I rewiind and try again.
In the distant past, my Mac was underpowered in many ways. The solution there was to create a dedicated 13GB partition to import to. I would wipe it clean just before an import.
The only cable problem I've had with one of my Macs was with the iSight firewire cable suddenly causing panics after I installed a USB 2 card. Using a different cable solved that issue.
Oh. When you ask these kind of questions, you should let people know more about your Mac setup (Model, internal or external import drive and speed if a laptop size drive) and camera.
