There is no button to mute the source window. There are times when other audio is playing and I do not wish to hear the playback from the source window preview because it's not needed. But there's no way to turn it off, or pot it down.
To be clear, this is not the same as "Mute While Scrubbing" which already exists as an option.
Often footage contains ambient sound/noise that isnt necessary to be heard during assembly, or at all.

Please give us the simple option to Mute the Source Window!!!