When you are in the messages app (this also happens on Facebook app) and you recieve a new message a sound will play even if you're looking at the thread where the new message came in. How do I disable it? It's very annoying and battery consuming for no good whatsoever. Any help is appretiated. Regards, Rodrigo.
In the Settings App -> Notifications -> Facebook you can turn "sounds" off.
This will also turn off vibrations.
It will not distinguish between whether the app is currently running or not, it'll just always be off. If you want that, then you will have to send an email to facebook requesting they change how their app works.