Technically what's going on... (let me know if this helps)

When a site creates a notification, there's no built in way to say "present this notification, and make the bing-bong noise".2. Some sites (e.g. skype) really want a sound to play, so when presenting a notification, the do two things...  

  1. Show the notification  
  2. Play a sound file in the tab

What Wavebox does is...

  1. Look out for when notifications are shown, and we play a sound file to accompany it... giving the user the expected behaviour of a notification & a sound
  2. At the moment, when a site plays a sound, we don't have any way of detecting if it's an audio clip (say Spotify), or a notification bing, or a video that's playing. The only thing we have our end is to mute the tab completely.Then when we stop notifications, there's not a way to say to the page "hey, that notification you asked to send, we threw it away", so the page just believes the notification got shown... and carries on to play the sound.
    This means, that although we can stop the notifications and the sound that we elect to play, we don't have a way of stopping the site from playing the sound that it thinks should go along with the notification.