Audio problem: When we see the first defence against the dark arts class with the pixies taking over, when Lockhart goes out and tells Harry, Ron and Hermione to pop them back into the cage, Hermione makes them all freeze in mid-air. Most of the pixies drop bits of paper, but one drops a big book. You can see it go thundering down the the ground, but you can't hear it land. All you can hear is bits of paper flying everywhere.
Audio problem: Riddle tells young Hagrid in the close-up, "They'll have your wand for this Hagrid. You'll be expelled." In the following side shot Riddle's mouth still moves as Hagrid puts his head down and though no words are heard his lips move as if repeating "You'll be expelled." It is not until the next shot of Harry as he yells, "Hagrid!" that the memory just begins to end as Harry moves back to the present.
Audio problem: At the Burrow, as Harry walks away from the clock, he notices the self knitting needles, in the wide shot as Ron passes the clock, he mouths the words, "It's not much," but nothing is heard. Obviously because it is meant to be heard in one of the following close-ups of Harry when Ron says, "It's not much, but it's home."
Audio problem: When Harry, Hermione and Ron discuss Tom Riddle and Hagrid's supposed link to the Chamber of Secrets Hagrid overhears something and asks if they were talking about him. Harry, Hermione and Ron all turn round and we hear them say, "No!" at the same time. If you watch carefully, Hermione says, "No!" slightly afterwards, but no sound comes out. The line has been dubbed so that they all say it in unison.
Audio problem: When the boys sneak into the Weasley house, while Harry walks over to the clock, one of the other boys whispers, "Do you think it'd be alright if we had some of these?" meaning the biscuits on the table, to which another replies, "Yeah. Mum will never know." The problem is, none of the boys are mouthing any of these words.