I have a 27" Cinema LED display from last year. It uses displayport, not thunderbolt. I have a new MacBook Pro with thunderbolt. I plug in the display's displayport cable to the laptop's thunderbolt output. In "Properties | Sound" I have "LED Cinema Display" selected, and nothing muted. PROBLEM: sometimes I get no audio. Spotify plays fine sometimes, youtube videos never. When Spotify audio is absent, I unplug/replug the display a once or twice to get it to work. For some reason, this doesn't work for youtube videos. ??? What to do?