the problem is that 10.10.2 is a piece of junk. look through the discussions, and there are already a number of them mentioning this. in all the posts i've read, this started with that update. amazing that apple can cause a problem that can both damage hearing and equipment, and after a month still nothing. i've had it happen about 5 times today. add to that, my bluetooth keyboard has disconnected and reconnected 30 times, often consecutively.
the only fix is disconnect the device, and reconnect. or, if you just mute audio and wait a number of minutes it is usually gone after un-muting. 10.10.2 is a failure. fingers crossed 10.10.3 fixes it. hope my speakers don't blowout in the meantime.