Shoutbox

I'm not sure if this is just because I'm using tabbed chats or whether its for something else, but when i'm talking to people, sometimes the alert sound (the sound when someone sends another message) goes off and sometimes it doesnt and i can seem to work out why?  Is this just because I am using tabs or is it something else. Cause its very annoying

I don't think that has anything to do with tabs. The same use to happen to me before I used Plus! and it still does happen. Very annoying, don't know why it does it