Then try this: When you want to mute the music, select it and press CONTROL-B (Clip Disable). when you want it back, select it again and press CONTROL-B again (toggle - Clip Enable). This method is a lot faster and costs you less render files, because you don't have to turn off music clips that are on the same tracks down the timeline. Also, there's a shortcut, and also you can simply Undo it or Redo it.
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