I recently upgraded to Mac Mavericks and from day one audio output disappears and returns at random intervals for short moments at a time. Sometimes, I'm in meetings on Skype calls, and the audio would just disappear, and it's extremely annoying when listening to music. My machine is a Late 2011 17" MacBook Pro. I always have my external Logitech speakers plugged into the audio socket. I normally run my machine in clamshell mode with an external HDMI Samsung monitor, however, it does not appear that the audio bug is caused by running in clamshell mode. I made a bit of a discovery today, as I happened to have the System Preferences open on Sound. I noticed that when the audio disappears, the box labeled: Select a device for sound output switches randomly between Optical Built-In ...and then back to Headphone Port upon which the audio returns to normal. I've been so desperate to solve this issue, that I even formatted my machine (which was long overdue) and reinstalled Mac Mavericks from scratch. This didn't help at all, the problem still persists. Does anyone have an idea what is causing this, and how to fix?