I have the same problem. I believe it started a few days ago when I unplugged a "Mini Display port to HDMI cable" from my MacBook Pro during a FaceTime call. Immediately after I unplugged the cable, I was unable able to hear the person on the other end of the call, and my computer started to make loud clicking sounds at random. During this time the video remained at full quality and the other user was still able to hear me clearly.
When I plugged my computer back into my TV, the audio started working again.
This afternoon another individual sent me a FaceTime call which I received on my MacBook Pro. Unfortunately, when I accepted the call at my desk I ran into the same problem, but this time I had no extra peripherals initially connected.
I just recently had a friend call me while I was trying to troubleshoot the problem, and found that the audio returns when I connect an external pair of speakers with a auxiliary cable.
At this point the audio seems to work fine when I set the audio output to anything but the internal speakers.
Any advice or insight? Anyone able to duplicate the results?