Comment 37 for bug 883485

See bug#8194 at bugzilla.xfce.org. I suggest you ditch xfce4-volumed. It's buggy, and (worse) it's a black box, without even a manpage. I disabled it via Settings==>Session-Startup==>AppAutoStart. Also make sure to disable Session-Startup==>Advanced==>LaunchGnomeSvcs. Then I was free to program the XF86Audio keys as I wished.

Shell scripts are actually a superior solution for this problem as they are both flexible and allow the user to see what's going on.
So I use the scripts I wrote: http://user.cavenet.com/rolandl/PulseAudioScripts.tgz These are toggle-mute, volume-up, and
volume-down, with zenity for notifications. This allows users to reposition notifications as desired, change their properties, or
eliminate onscreen notifications if they want.

Don't try to solve this problem. Use the shell scripts. Even simpler: program the XF86Audio keys for 'amixer set Master
5%+, or 5%-, or toggle. A black box solution is no solution at all.