Audio problem: After Barney falls over in his chair, you can hear him say, "Hmm, a pretzel." His mouth doesn't move. (00:21:15)
Audio problem: When Otto says that he was on his way to Mexico, his mouth doesn't move in the interior shot of the bus. (00:04:20)
Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer