FCP7 playback jittery on new iMac
Editing a new FCP7 project on new iMac (late 2012 model, 27", 3.4 GHz Intel Core i7).
Playback (in both the Viewer and the Canvas) has an intermittent "rolling shutter"-like image. Sometimes it's there when I play a clip, and sometimes it isn't.
All of the original footage is fine, so something's happening in FCP.
I've tried various RT settings in the Timeline, but still have the problem.
Any ideas to fix this?
iMac (27-inch, Late 2012), OS X Mountain Lion (10.8.3)