Quicktime skipping / getting hung up during playback
I use Final Cut Studio a lot. This is a new system. When I playback either through FCP5 or Quicktime 7, videos I create, even trailers I download from Quicktime.com, sometimes get hung up during playback. Playback doesn't stop, but it's almost as if the video will temporarily lag, or stop in mid-playback, as if there are too many processes running. Kinda silly though -- it'll happen after a fresh reboot, with nothing else running. I even reformatted and reinstalled OS X, in hopes that it was some software glitch I couldn't figure out. Didn't help. I ran hardware tests from the OS X install disc -- everything passed.
Has anyone else experienced this? Does anybody know what my problem could be?