Unfortunately, there isn't a way to turn of this bloody annoying sound with the normal settings - you can root your device, but most users don't know how (or don't want to) do that - me included. Luckily, someone has created a nice little app especially for the Galaxy S2, that mutes your phone just before it gets fully charged. It even has some settings, like when you want the app to be "active" and so on.
Aside from that, it doesn't do anything else, but it's a great app if you charge the phone overnight in your room when you sleep.
Get it here
Till next time!
