Audio problem: In the car, when Homer accidentally kicks the horn twice, the second noise goes longer than it's supposed to. (00:08:10)
Audio problem: When the old lady is playing the keyboard at Homer and Marge's wedding, her hands don't match the music.
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