Burns Verkaufen der Kraftwerk - S3-E11
Audio problem: When the drunks find out they're going to Hawaii, one of them says "Maybe I'll marry Elizabeth Taylor." If you look at their mouths, though, they don't move right. (00:09:50)
Burns Verkaufen der Kraftwerk - S3-E11
Audio problem: When Horst is checking the power plant, he sees some radioactive liquid pouring out of the chimney, he says "That shouldn't be" but his mouth doesn't move when he says "be". When he spots the raccoons he speaks but his mouth does not move at all. And at the end when Mr Burns is mocking the German men, Horst says "Burns, stop it." but his mouth doesn't move. (00:15:30)
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