Audio problem: In the very first scene of the movie when Bobby is recreating his performance at the Coconut Grove, the actions of the band are out of sync with the music we hear. (Bobby is in sync, but the band is not.) Watch the hands of the drummer and the band leader: The entire scene is out of sync, but when the drummer moves to the ride cymbal you can easily see he is ahead of the music, and when the band leader gives the band cues for accents, his hand movements are behind the music and therefore happen too late.
Audio problem: During the scene at the AVN convention, when Matt sees Danielle by her big poster dancing and signing autographs for a group of fans, he walks over and starts pleading his true feelings and asks her to come down and talk to him. Right as he pleads, "This is all my fault", the camera shot slightly to the left and behind Matt does not show his lips moving at all.
Audio problem: In the scene where Jack returns to the motel in the morning (after his first night with Stephanie), she's waiting for him on her motorcycle. When Jack goes back downstairs and gets on the back of the motorcycle, the sound effect is that of a revving bike engine, but you can see that Stephanie's right hand (the throttle hand) is not moving at all.