Did you try to play a new game and then load your old game to "kick start" the sound working again?
I didn't - I just tried pausing, saving, reloading, resetting and such. I've just got home, and started a new game, then reloaded the old game - problem solved.
The sound worked perfectly in the menus [the noise when you scroll the start menu] and at the title screen, so I knew it wasn't a hardware issue.
So if anyone else experiences this problem - start a new game, load the old game. Hopefully this works reliably, and anyone who has this problem can find this thread [I searched all kinds of key words to try find a solution to this problem].
