Pulsing pixelation in certain shots on dvd
 

I been trying to make a NTSC version of a program I shot in PAL. I noticed the appearance of a pulsing pixelation, maybe every fourth frame, but only in certain shots. The image appears to pixelate, at regular intervals, giving a pulsing appearance

Today I made a PAL copy of my program, using compressor and dvdsp, and I found the PAL dvd also has pulsing in certain shots. It is not seen across the same shot, and when it starts, it appears to get worst, even going into the next shot.

In compressor I have been using the default Best quality 90 min dvd setting, and making slight adjustments for my 75 min project (setting av bit rate to 6.5)

In DVDsp I was using the factory settings, just making changes to 16:9 setting.

I have previously produced idvd dvd's with no problem, and decided to give dvdsp a go with this production.

Has anyone experienced this pulsing pixelation problem? Can anyone suggest a way to remedy it?