I have this exact problem, I have a late 2008 macbook pro, with a Samsung syncmaster p2050 set as a dual display. When in final cut I have just the monitor window showing on the monitor, I edited something this morning just fine, no problems. But I’ve just started a new project and when playing back on the time line it flickers between 2 frames from the shot. It’s not the monitor and it’s not the cable..
Any help is greatly appreciated.