Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: In the opening when Marge is warning us about how bad this years episode is, her mouth barely matches what she says.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: Right after Flanders makes his first wish, when Moe chases the alien, Moe is talking, but his mouth doesn't move. (00:08:00)
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When Kang and Kodos land in Springfield and hit Mayor Quimby with a club, one of them says something but his mouth is not moving.
Tree House of Horror II: A Simpsons Halloween - S3-E7
Audio problem: When the guy who Homer buys the monkey's paw from tells him that he'll be sorry, his mouth doesn't move. (00:03:10)
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