I couldn't find the find the export in the project folder but what I did notice is that fcp kept on pulsing rendering, like every second a pulse on, then off, with high cpu load- which is not normal. So if I cut the movie and delete a portion then the rendering stopped- i.e. I was cutting out the bad frame(s) like Striken says. but initially, the cut portion was way too much so I kept splitting the bad part in half to zoom into the trouble spot (undoing after each cut, to restore the full video) until I had zoomed in far enough, basically full zoom, and I could see the missing video frame or maybe two, in the editing window. They were just black, the audio was intact. So I got to delete just that bad frame and now all is good. Took just a couple of minutes to do this...