That's called "dramatic license". We don't need the audio cue to tell us that Vader was told the ship is clear. We see the ship clear, then we see Vader go to talk to Palp. Why else would he be moving?
Or Vader just don't want the Emperor to wait. He goes right in the room placed next to his chamber. If the transmition is not clear yet, he'll just choke one or two imperial officers...
Never had any problem with that scene.