Facebook is testing out a couple of new features: a notification sound and comment replies. The notification sound and comment replies are currently only being tested out with a select number of people. It is uncertain whether Facebook will roll out both changes to the whole community or not.
The Facebook comment replies makes it easier for people to respond to individual comments rather than the whole thread. This makes the discussion easier to read too.
NEW! Facebook now allows you to directly reply to a comment on the post. This is brilliant and simple. twitter.com/PavelNovel/sta?
— Pavel Konoplenko (@PavelNovel) November 9, 2012
The notification sound reminds me of how the Twitter reader application TweetDeck plays a chirping noise when there are new tweets that have popped up. This is a great way to keep people engaged, but it can get annoying pretty fast. I disabled the noise on TweetDeck right away.