But then you go into 'ringtones + sounds' (mix some maths with some English - and it's on many other items. Could we not just have 'and' ???))
And in there, 'manage app sounds'.
(which is the same as going, settings, 'notifications + actions' (or on my 1520, I can't see the "s" on actions - phone must be too small). Ah, so that's why they use a "+".)
And in 'manage app sounds' ('notifications + actions'), there's all the things that you can have sounds for. So picking one, anything; and then the "Notification sound" for that - there's one, second to the top of the list, called 'default'.
What sound is that? And where do I find it? And why can't I "play" it? (then I could maybe find out).