Who Mourns for Adonais? - S2-E2
Audio problem: At the temple, as Kirk goes to call the ship, he flips the communicator to open it, as he usually does. However, he has to flip it twice to get it to open, but the sound of the channel opening is heard from the second he starts.
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.