I've noticed that when I playback some footage on LCD or in my editor, there is are sudden frames of white flashes that surge through the frame, it doesn't fill up the frame either, sometimes it just covers half a frame, and then moves up a tad.

It's so annyoing! It feels like a visual and mental stutter everytime i see it.

Has anyone else experienced this with their Mark II, or is this some hardware issue that I should get resolved directly through Canon?

Sounds like a camera flashbulb while you're shooting progressive. It's just a downside of the 5D. Give those still photogs a dirty look. :-)

Are there people around you taking still pictures with flash while you're rolling video?

I'll be sure to give those photogs the stink eye. I think for my recent project it is the camera flashbulb that's the issue. I went into FCP and looked frame by frame, and you guys were right.

I could have sworn I noticed it in other shoots too where there are no flashes around the area.

Though there is a stutter when I first hit record in the footage, almost like a brief pause to black, I'm assuming that's normal right? (therefore just make sure you never use the first 2-3 seconds of a shot)

Thanks for the fast responses guys!