This problem occurs if your broadcaster software plays the sound source of your desktop to the stream as well. As a result, it will play both the actual audio track and the audio track from the Stream Manager's action.The best thing to do is to mute all audio sources and activate only your microphone. You can still hear the sound of the movie or series if you click on "Open Watch Party in a new tab" below the stream window. This will give you the same view and audio track as your viewers.