Looking for a little bit help here. I've searched everywhere and couldn't find an answer. My 2013 27" iMac doesn't play sound with the speakers (movies, youtube, itunes, etc..) but when I go to "Preferences" and "audio" and click on any of the sound effects there, the effects are played trough the speakers. I can't turn off the "mute" option on that preference panel. Any idea how to solve this problem?