Audio out of sync on some ripped DVDs, not all

[mischugenah]

I'm ripping a bunch of DVDs for a trip, and most of them rip and play back just fine. A few of them, though, end up with the sound and video badly out of sync, sometimes as much as 15-20 seconds. It seems to be an issue with how the first part of the DVD encodes, because if I save just (for example) chapter 3, it syncs fine, but chapter 1, even when recorded alone, is seriously off. Any ideas on how to fix this?
Thanks!