Hard to say, could be many things depending upon what you've loaded on the phone for apps. Facebook can be a pain as they have a notification for so many things.
One sure fire way to control all your notifications is to use an app called Light Flow. Initially developed to control your notification light with different colors it has since grown to also allow the use of custom notification sounds and vibration patterns. Very powerful app.
Once you have this app you just turn off your stock notifications in the settings and assign different colored lights, sounds and/or vibration patterns for only those app notifications you want to receive notifications for.
There is a free version that will allow you to test the app and see if it's for you. Paid version (only $1.99 last time I checked) adds a whole bunch of addition apps. The dev is very responsive to questions and suggestions.