dbus-monitor --session "type='signal',interface='org.freedesktop.ScreenSaver'" |
  while read x; do
    case "$x" in 
      # You can call your desired script in the following line instead of the echo:
      *"boolean true"*) echo SCREEN_LOCKED;;
      *"boolean false"*) sh -c "echo SCREEN_UNLOCKED; pulseaudio -k";;  
  done &

Have this run when starting Gnome/KDE etc seems to work okay.

It isn't ideal. Saves you running pulseaudio -k manually, that's all.