Comment 2 for bug 654323

I also have this problem at the moment. The sound has worked fine in the past, including after I installed 10.10. But about a week ago I had this problem. I didn't investigate it and it was gone the next day. Yesterday I had it again, and it's still present today, after shutting down the computer overnight. The sound can be unmuted as long as no application is playing sound. But as soon as something produces sound, it mutes again immediately. Attempting to unmute while sound is playing just produces sound for a fraction of a second and then it automatically remutes.