On my Macbook, some of the sound has stopped working. The volume works and everything, but things that have stopped making sounds are things like, when i take a screen shot, it doesn't make that little noise anymore. The same with Photo Booth. When I press to take a photo, it doesn't make the "flash" sound after it takes it...I haven't fiddled with anything lately and have no idea why this suddenly happened. Anyone have any idea how to fix this?