Audio problem: During the scene with the "flying" letters Harry gets one letter and tries to go in his "room", but Uncle Vernon grabs him. When Harry yells "They're my letters," not only his mouth doesn't move but his voice sounds much deeper than in the rest of the movie (it sounds more like his voice in Chamber of Secrets). This indicates that this line was overdubbed long after the main filming, when Daniel Radcliffe's voice has already begun to change. (00:11:55)
Audio problem: When they arrive at "The Magic Carpet" you can hear Izzy drag three heavy bolts across the door, when the door opens, there are no bolts - just as well, otherwise shooting the lock wouldn't have worked. (00:56:30)
Audio problem: When Arwen and Aragorn are talking on the bridge, you see Arwen's lips moving while Aragorn is speaking. When you zoom in you can see that Arwen's mouth is definitely moving as she is talking animatedly, both when neither character has any dialogue and when Aragorn's voice says 'I thought I had strayed into a dream'. (01:32:15)
Audio problem: When we see Mike during the slumber party, we hear seven bells ring for the seven filled cylinders, but there are only six cylinder-filling noises. (00:16:50)
Audio problem: When Hal is talking to Katrina, after he's been de-hypnotized, in the over-the-shoulder shot of him facing her, we hear him talking but his mouth doesn't start moving until he turns to look away from her.