Audio problem: Right after the Jamaicans are massacred in the office tower, a bunch of reporters are all broadcasting from the scene. The camera moves along a row of them. Their mouths aren't in sync with what they are saying. (00:25:50)
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: In the final scene as the rescue helicopter is landing you can hear its engine spooling down; however the helicopter hasn't landed yet. As the helicopter takes off it does the opposite - you hear the engine spooling up, but the helicopter has already taken off.
Answer: The predators are honour bound hunters, and as such they will only attack a target if it is capable of defending itself (i.e, if it is armed, which is why it doesn't attack the boy in the cemetary). Although the police outside were armed as well, the Predator presumably attacked the drug dealers because they were a harder target (as the police were outside he could have just sniped them from the roof tops, but he had to get relatively close inside the building) and as such, killing them gave a higher honour. The obsession with Danny Glover's character is probably because he is quite a brave and heroic person, similar to a Predator (the way he saves the other cop by risking himself etc.), so the predator may have been studying him for a while. There's also more honour in killing someone like that (as he'd be a hard target) than there is in just killing a random armed guy.
Gary O'Reilly