Audio problem: When Herbie is pushing furniture on to the two security guards at the warehouse, the first security guard yells "Look out, Smitty! Run!" but his mouth does not move.
Audio problem: Pay phones are programmed to drop the coins into an internal storage box after the receiver is placed back in the cradle. But at the airport, when Whitfield hangs up on his mother (and he didn't call collect), there's no sound of coins dropping. (00:38:00)
Answer: I don't know specifically why these particular actors did not return. There are any number of reasons why an actor does not reprise a role in a sequel: salary disputes, creative differences, scheduling conflicts, an actor wishing to avoid being stereotyped, and so on.
raywest