Audio problem: Right after Bert kills the second graboid he gets on the radio and says "we killed that mother-humper". Val replies "...be advised there are two more mother-humpers". However Val's lips don't seem to be saying "humper". This occurs even in unedited versions of the film. (01:01:40)
Audio problem: Bruno's mouth is out of sync when he says "I really do hate margarine," as he is talking to the waitress about what are in the sandwiches that day.
Audio problem: When Kyle takes the knife from the closet and pulls it out of the leather, it makes a sound like metal scraping on metal. (00:50:45)
Audio problem: When the Predator is about to shoot Gary Busey, just before Danny Glover blows the door in, listen. The actor playing the Predator is counting to three before the explosion, preparing himself for the effect. Easily heard if you turn your tv up. (01:16:15)
Audio problem: When the angry cab driver is yelling at the female cop that stole his taxi, the words you can hear him saying do not match is mouth.
Audio problem: Right after the doctor falls in the basement he is talking about how no spiders are going to be there. Then he keeps repeating "Oh s***" but it looks like his lips are delayed.
Audio problem: This problem exists in the extended Director's Cut. When Narcisse is first introduced in the hospital, when we cut outside to Decker and the police walking to the room, they suddenly hear Narcisse grunting which makes them rush to his room. However, they are quite the distance from his room, and Narcisse's grunts are fairly low, so it's obvious they shouldn't have heard him from that distance. The audio mixing tries to make his grunts sound louder, but it doesn't sound right at all... they're way down the hall from the room, but his low grunts sound like they're coming directly right next to them. This is all the more confusing, as in the theatrical edition, they are alerted to a distant scream by a nurse, which was much more believable. (As the Director's Cut is currently the most readily-available version of the film on Blu-Ray online, and is the director's intended edition, I believe it should count as a mistake).