Sometimes while the video is playing the sound stops for a little while and then picks back up.
I will be watching a playback and the sound will stop, everything else keeps going but the sound almost "mutes" itself and then comes back on.
Will Simpson commented
I tried those before. Using no input, default, headphones etc. its not the audio output, it seems to be a glitch in the playback.
This bug has been around for years. It's actually better than it used to be believe it or not.
Matt Stegner commented
Are you on Windows or Mac?
Can you try setting the "Preferences>Audio Hardware>Default Input..." to No Input and see if that helps?