Comment 27 for bug 1001842

>After the 12.04 Update my HDMI audio stops working anytime I turn off or on, my 2nd monitor(plasma TV)

Try to comment the line in /etc/pulse/default.pa
load-module module-switch-on-port-available
and reboot or restart pulseaudio with
pulseaudio -k

Does it help? If not - revert changes by uncommenting the same line back.