Sure, I've added an option in the menu to mute it when the game/tab is unfocused. It's a secondary option on the master volume option for now, since there's not enough room to add it, until I get around to doing a proper overhaul of the settings screen. Unfortunately it doesn't work on the web version for some reason (I tried 3 different methods and none of them worked), but at least it'll be on the downloadable version. It'll be in the next update