Vidding discussion

I'm working with Premiere Pro 2, and when I export a movie and play it in VLCPlayer, sections with any significant horizontal motion get flickery white lines--sort of like slightly bad tracking on a VHS? It's not a huge distortion but it's visible and annoying, and the weird thing is it does NOT show up in the clip itself. Like, if I play the clip on its own in VLCP, it's fine, and when I'm watching the source window in Premiere, it looks fine. The lines only show up once the whole thing's been rendered. Also, this happens both with footage ripped from DVD *and* with clips from newer downloaded episodes of lower quality. I *think* it might only be happening on clips that have been slowed down, but it's not like I can...stop doing that. :(

Is there anything I can do about this?