Audio problem: Just as McClane and Farrell are about to leave the Eastern Power Hub, Farrell goes on a long rant and his mouth does not match the words he is saying. [In the unrated version of the film, the rant concurs with Will's mouth movements, but the mistake is valid for the regular version.]
Audio problem: Before they leave for Mission City, Lennox tells Keller, "Sir, you gotta figure out some way to get word out..." Then in the next shot, as Lennox shouts, "Let's move!" his mouth stays open - not forming the "m" with his lips to produce the word "move", which we hear very clearly (it looks as if he really said, "Let's go!"). Changes in dialogue are done during ADR and often are not in sync with mouth movements seen onscreen. (01:45:45)
Audio problem: During the scene where he is hitting golf balls off of the ship, he is hitting an iron. For anyone who plays golf, the sound that goes along with this is that of a driver or some type of fairway metal.
Audio problem: In the scene where Doyle, Scarlett and the kids jump into the Volvo estate to escape the gas and infected, a number of references are made to the car having a manual gearbox, i.e. "pop the clutch". Doyle puts the car into second gear and several shots of the gear lever are shown. However, when Doyle push starts the car and they drive off, listen carefully and you will hear the distinct sound of the gear change of an automatic box.