Audio problem: As Popeye Doyle is chasing the elevated train, he is continually honking his car's horn to warn pedestrians and whoever else to get out of his way. One scene shows him with one hand firmly on the wheel, and he hits the top-most rim of the wheel in frustration, and the horn honks on both hits. That car did not have a rim-blow type horn mechanism - only Fords had those, and this was a Pontiac Le Mans.
Audio problem: When Harry shoots Scorpio in the leg on the football field, as he walks towards him, Scorpio shouts out "Don't do anything more! No! No!" If you look at Scorpio's face, however, you can see his mouth is not moving in sync with what he is saying.
Audio problem: When the saxophonist talks to Eddie (Albert Finney) before joining his band, which has already started playing, the saxophone can be heard although the player has not yet joined them on stage.