Audio problem: Spock uses the intercom to call Mr. Scott who is in engineering. As the shot cuts to a side view of Scotty standing at the controls, he answers "Scott here" but his mouth or lips never move. (00:44:24)
Audio problem: When Chekov goes berserk on the bridge, he emits a scream and shoves Spock. When Spock holds Chekov's face, the closeup on Chekov shows a scared look, and the original scream is played again, but Checkov's mouth doesn't match.
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.