Sorry. I should have been more clear.
I think we were confusing the word render (I work mainly in AE) I’d pressed “enter” which apparently wasn’t rendering all the clips, just the red line areas (artwork). The video clips remained with yellow lines. After I completely rendered the clips in the time line there was no flickering on playback within premiere.
No noticeable issues frame by frame.
Reading files from external drive (Firewire 800).
Previewed as described above and playback was flawless.
I exported 2 clips (422 & mp4) Both had no flickering and no visible issues.
Looks like the issue is when the video clips have yellow lines above them, some sort of realtime preview glitch. I don’t think it’s happened before with codecs other than h.264 in my case. It happens sporadically but now that I know when I completely render the timeline I can they disappear I can edit with confidence.
Thanks for your speedy replies and assistance.