Audio problem: After the scene where the men had to fight off the giant bugs, there is a wide shot where the men can be seen being helped out of the pit by the captain and a few extra crewmembers. The captain is shouting something, however, if you look closely, his mouth is not in sync with what he is saying.
Audio problem: When Carl tells Preston to show Ann on board the ship he says something like, "Hello, Miss Darrow, I'm Mr. Denham's assistant." His lips aren't properly synchronized with the dialogue when he says this.
Audio problem: When the ladder Ann was standing on hits the ridgy part of the Empire State Building there is no loud crash.
Chosen answer: The original creator of King Kong, Merin C. Cooper, wrote a novel adaption of the movie in which it was explained that the gates were built by a earlier culture of islanders that were friends with the "Kong" race. The "Kongs" helped the original islanders to build their village and the wall (thus meaning the gate had to be big enough for the giant gorillas to walk through). By the time of the events of the movie, the original islanders have "died out" and their old village had been taken over by a race of more primitive natives who became enemies with the Kongs, and were trying to use the gates for safety.