Apple has released a software update designed to fix intermittent audio loss issue experienced by some users of the 27-inch LED Cinema Displays.
This Firmware Update addresses intermittent audio issues some users have experienced while using the 27-inch LED Cinema Display.
The updater application will be installed in the /Applications/Utilities folder and will be launched automatically. Please follow the instructions in the updater application to complete the update process.
It requries 10.6.4 + LED Cinema Display Software Update 1.0 (or 10.6.5 or later).
"You may notice that sound from an LED Cinema Display (27-inch) connected to a Mac intermittently becomes inaudible. In some circumstances, you may need to unplug the display and reconnect it or restart the Mac before the sound becomes audible again."
Download From: KBDL1338