well, what
did you compress it to?
also it *could* be due to pull down.
as you now i deal with PAL footage mainly and don't normal have to deal with 23.976 or 29.97
so take the following with a grain of salt.
once i did have to rip an old film from an NTSC DVD, and got lots of feild issues.
i had to go though and figure out the field cadences, and run the clip through Cinema Tools to reverse telecine.
at least i think that's what i did it was a while ago, and as i say, i don't do this every day
there were sections within the file where the cadences changed (don't ask me why, i guess it had been edited after it had been telecined)
so i had to batch export it into smaller chunks, and reverse Telecine each of them.
nick