indicator-sound is broken in XFCE, currently.
To fix this, you can edit /usr/share/dbus-1/services/indicator-sound.service
sudo gedit /usr/share/dbus-1/services/indicator-sound.service
And change the content to this :
Exec=/bin/sh -c 'if [ -n "$(ps -U $USER | grep xfce4-panel)" ]; then
This will load indicator-sound-gtk2 when using XFCE session, and use indicator-sound when another session (like Unity) is loaded.
I'm currently using Arch, but maybe this will help you :
As you can see, it works for me. But interresting fact : it's not named indicator-multiload but xfce4-systemload-plugin. I think this plugin comes with xfce4-goodies package.
That might be the indicator you'r looking for ?