Audio problem: Throughout the final sequence, when Harry and Nora are in the jeep and being chased by the police cars onto the field by the gym, many of the words Harry says are out of sync with his mouth.
Audio problem: Just about every time someone starts or stops a cassette tape, we can see that they're either faking it or pressing the wrong button. In one shot, the 'Pause' button is down both before and after the actor presses 'Play,' which would of course mean that the tape shouldn't play at all.
Audio problem: When Nora is trying to tell Mark that it wasn't his fault that the boy committed suicide, her lips aren't in sync with what she is saying. (00:38:00)
Audio problem: When the reporter is filming the punk lighting smoke bombs in front of the school, he is encouraging his camera man to film the punk. His mouth doesn't match what he's saying briefly.
Audio problem: Near the end when Mark is shouting for the kids to start their own stations, in the wide shot the audio doesn't match up that well with what he's saying.
Audio problem: Around half an hour into the film, some kids are listening to a tape of the radio show and a teacher takes the tape out because he doesn't like the content. As he takes the tape out, the audio ends right after the tape door opens, when it should have ended a little sooner, if it was actually coming from the tape player. (00:32:35)
Answer: The first time I watched the movie, I kept thinking that Mark's parents were going to hear him and catch "Harry" in the act. When the girl was with Mark, Mark's parents pounded on the outside door; when Mark opened the door, his parents said they thought they heard him talking to someone. So, from outside the garage door, someone might be able to hear muffled voices but not the actual words. Why his parents cannot hear him in the basement when they are indoors lies in the props/scenery plus some inference. The numerous objects in the room (tapes, CDs, albums, guitar, drums, bongo drums, recording instruments, amps, etc.) indicate that Mark is into music - loud music - and electronics. He apparently was given garage/utility storage space to turn into essentially a studio for himself and a place to play his drums and music without disturbing his parents. The space has been sound-proofed - thick concrete walls, insulation, and cloth wall hangings to deaden the sound.
KeyZOid