Audio problem: After Johnny escapes into the city, Ben returns home and starts to shout at Fred for letting him get out. Watch Freds mouth closely as he replies, some of the words he says back to Ben have been removed. Judging by his mouth movements, they appear to be swear words he is saying, and as the film is rated as PG, they were probably removed so they would not cause offence.
Audio problem: Quite a few scenes in the film appear to have been dubbed over. Most of them are at the start after Ben and Fred have to keep Johnny 5 indoors. The mouth movements don't seem to match up with what is being said. If you look at the mouth's of the actors, there appears to be quite a few strong swearwords in the film, which were probably removed because it's a kids film.