The issue in question involves audio from the display’s speakers dying intermittently. In order to fix the sound issues, users have resorted to unplugging and replugging the monitor’s USB cable—or, in other cases, even rebooting their Mac. This firmware update should, hopefully, zap that bug and return order to the galaxy.
To update the firmware, you can download the 957KB updater from Apple’s support download site or via Software Update and then run it from your /Applications/Utilities folder. If your display’s firmware is already updated, you’ll get a message to that effect, and you can go about your business. In order to run it, you’ll need a Mac running Mac OS X 10.6.4 with the LED Cinema Display Software Update 1.0 or Mac OS X 10.6.5 or later.