Audio problem: The police officers chase Arthur to the subway. When the subway train starts moving after they just barely got in, the sound resembles the acceleration sound of a R143 subway car, which actually didn't exist until 2001, but it's a much older car, the R32.
Audio problem: In a bit of movie magic, nobody touches the TV set in the dressing room, but it adjusts its volume perfectly by itself, to the point that not only does not disturb the conversation with Murray and the producer, but even when Arthur is all on his own and sits back in his chair the TV, still turned on and showing a program, is perfectly silent. (01:35:10)
Answer: This is later, as the building appears to be Arkham. He's committed there instead of going to jail based on his insanity. It appears he is laughing about the death of Thomas Wayne, we see a flash of that scene again for a reason.
lionhead