On each boot, an incorrect audio output device is selected, at least when HDMI audio output is in use (still need to test the TV/aux output; will update the bug when done).
Specifically, the settings application lists "Multichannel Output - Built-in Audio" as the selected output device. However, for audio to play through the connected HDMI device, "Analog Output - Built-in Audio" must be selected instead. Unfortunately, this setting will be lost on subsequent boots. A workaround is to remove the following lines from /etc/pulse/default.pa:
### Use hot-plugged devices like Bluetooth or USB automatically (LP: #1702794)
.ifexists module-switch-on-connect.so
load-module module-switch-on-connect
.endif
However, removal of these lines will (as the comment suggests) result in hot-plugged USB devices *not* being automatically selected.
This bug has been reported on the Ubuntu ISO testing tracker.
A list of all reports related to this bug can be found here:
http://