Clip's video momentarily freezes during playback

Question

When playing a clip from the Clip library or in the Project timeline the application will periodically freeze; any keyboard inputs (such as hitting 'K' or 'L' during playback) are buffered. Everything on the screen freezes but the audio continues to play. After a couple of seconds the application will unfreeze and the video will "catch up" with the audio. The buffered keystrokes will then take affect.
(It's possible to skim the clip and it will not freeze during this. Skimming backwards and forwards at variable speeds works without a problem.)
For example, I choose a clip that is 11:37:44 in length. The first time the clip is played it freezes about 6 seconds in, then unfreezes 3 seconds later. The second time it doesn't freeze at all but plays straight through. The third time the clip is played it freezes about 4 seconds in and then unfreezes.
It's the random nature of the problem that is so vexing.
I'm running FCPX Trial 10.6.0 on a MacPro 1,1 with 16GB of RAM, running 10.7.5 and using a 2TB eSATA-connected RAID 10 drive. The OWC enclosure is fed by a SeriTek/2ME4 PCI card and the MacPro has been upgraded to an NVIDIA GeForce 8800 GT graphics card. There is 584.29 GB available out of the 2TB.

Answer 1

I logged out and logged in as a different user. I fired up FCPX and imported the same event file from the book.
It did not freeze once during playback.
I then imported one of the clips (.mov) I had imported from tape. Again, no problem whatsoever.
I removed any applications launched during log-in and logged in as normal, launched FCPX and it still exhibited the same problem with freezing.
Since all of the media is on the same (RAID 10) disk and the only difference is the account I've logged in with, it appears that there is a process running under one account that is responsible for the momentary freezing. If I find what it is I'll report back.