A lot of Ubuntu users can't get the old classic Wolfenstein ET to work with sound, but I have good news - I know a fix that works every time.
wget -q -O - http://nullkey.kapsi.fi/et-sdl-sound/et-sdl-sound.gz | gzip -d > et-sdl-sound && chmod a+x et-sdl-sound
then we need to edit the file from the old alsa sound system to our new pulse sound system:
sudo gedit /home/yourusername/et-sdl-sound
Go to line 40 and the change the line from this:
SDL_AUDIODRIVER="alsa"
to this:
SDL_AUDIODRIVER="pulse"
save the file and close and then you need to make a symbol link, so you can play the game:
/home/yourusername//et-sdl-sound
I hope it works for you, enjoy.