Trouble encoding video in Burn

I've edited together an hour long wedding video in FCE that I filmed on my Canon 550d at 24fps. At some points in the video I've used slow motion and speeding up effects. I've exported the film fine and Burn has encoded the film with chapter markers no problem.

The problem I have is in the mpeg2 encoded version at every point that I've adjusted the speed horizontal waves come up across the picture. I know for more effective slow mo I should film at a higher frame rate, but it was fine in the exported version.

I've added conversion markers on the adjusted frames and made any adjustment I can in Burn, but to no avail. Everything else has turned out well and looks good apart from these frames that have the speed adjusted.

Any ideas what I'm doing wrong?

Any help is hugely appreciated.

Thank you

Sam

I filmed it on my 1920 x 1080 24fps setting and exported it at the same dimensions. The whole video is fine apart from the slowed or sped up bits.

Thanks