Chat Rooms: How can I turn off sound in the chat rooms?

When you use the chat rooms, we'll play a sound when someone joins or leaves the room and when someone says something. This way, you can keep searching for your match without missing the latest happenings in the chat room. 

If you aren't a fan of the sound, you can turn it off by clicking on the speaker button from the chat room options in the upper right corner of the chat room window.