I have been having this problem, and it seems to be somewhat common amongst other ATV3 users. I get a video going on my MBA, try to mirror it up to my TV...the video mirrors just fine, but the audio continues to come out of the MBA speakers rather than the TV. However, if I turn the volume up or down, the little "audio up and down squeak tone" comes from the TV. I have had this happen in the past and I would just restart the ATV3 and that would usually fix it (actually I would just put it to sleep rather than doing the full restart). Sometimes I would have to sleep/wake it a couple times, but it would eventually work. Last night I tried and tried and tried, sleep/wake like 10 times, manually restarted the ATV like 5 times, restarted the MBA, disconnected and reconnected wifi, everything, and I just couldn't get the audio to mirror to the TV. Finally I just gave up and decided to watch the video on the MBA. Is there any sort of fix for this other than restarting? FWIW I have a 2012 MBA, ATV3, and a regular old Netgear router.