Audio problem: When the helicopter lands and the teenagers cheer you can hear dialogue from later in the film in the background. Several times you hear "Sean, catch the rope." which they yell later in the movie.
Audio problem: Right after Hooper says "Bye bye, nice officer." and activates the rocket system, the cop driving beside them screams "Great God almighty.". Watch the cop's rear view mirror when he yells that - it's a completely different person in the mirror and his mouth doesn't move at all, much less yell "Great God almighty." But when he calls "Headquarters. never mind", on the radio, the original cop is shown again.
Audio problem: At the bar after the tall black man asks to dance with the boys' dates, he lifts the booth table up off the floor. There's a sound like it's being forcibly ripped out of the floor, yet the table has a round bottom with no visible bolts or screws. While it may have been heavy, it wasn't secured to the floor.