RuneScape already has some very basic ambient noises. You can hear duck's "quack," sheep "baa," cows "moo" and kittens "meow." It's very basic, but it's a start. I don't think it would be too hard to put in more, like hearing the ocean when you're along a shoreline, or hearing distant moans, or the drip-drip of water while in a dungeon. Just because it is a .midi, doesn't mean that these sounds can not be made, it would just take some finesse. Whoever composes the RuneScape music could definately do it though, because there is talent there if you've ever actually listened to some of the songs.