Audio problem: In the scene where Todd is in the principal's office with his parents and the principal, and is is being asked to sign the paper, during the shot of Todd looking at the paper, his father's voice says," I've had enough, just sign it", and it is very obvious that line was added in because it sounded like it was very distant or over a radio or something.
Audio problem: In the classroom when Keating says, "Armies of academics going forth measuring poetry.", it is obvious that this is dubbed over because his mouth doesn't move correctly with the words.
Audio problem: When Chet is pummeling Knox, Chris pulls him off yelling "Stop it!", but her mouth doesn't move.