"Da-do!" Someone just liked your status!
Facebook thinks that the visual cue of that little red number at the top left corner may not be enough, so they're testing a new feature that would guarantee you never miss another notification.
VentureBeat confirms that Facebook is pushing new notification sounds to a small set of users.
Here's what they sound like in action:
If you truly hate the idea of Facebook playing a sound every time you get a notification, think about it this way: it's more likely that they will scrap it as opposed to roll it out worldwide. Facebook performs small tests with new features all the time, and only a small percentage ever come to fruition. In the last few months, we've told you about tests for notifications for declined invites, thumbnails for photo-related notifications, and reminder notifications that pop up an hour before a scheduled event. So far none of these have seen primetime play. As it stands, sound notifications are just a small test.
Plus, if they do roll out to all users, you'll be able to turn them off in your notification settings with a single click.