Facebook app and the Facebook Messenger app often plays the same sound for new incoming chat message - this is the system notification sound.
That makes me confused facebook chat with other notification, especially the calendar reminder, new incoming email, etc. ...
How to customize it?
In Facebook, you can change the notification sound from Facebook > Menu > Settings > Notification ringtone.
I assume it would be the same for Messenger, never used it though
Go on messenger select a ringtone I just did it because Eveytime I have to update messenger I have no ringtone. Then for facebook go in Facebook settings choose a different ringtone. Have different ringtone for both. On messenger there there is a little icon tap on it you will see your ringtones
