When playing and doing some other things in another tab (for exemple videos from youtube), that beep is annoying but usefull, so volume slider (under "sound: on/off" button) would be great solution for that. If you like this, please vote in feedback:

http://warlight.uservoice.com/forums/77051-warlight-features/suggestions/2147635-volume-control-slider?ref=title

thanks...