Description:
There is a condition in the pulseaudio xinit-script that should check whether pulseaudio will be started by XDG autostart. At least in my case it does not work. $SESSION variable is empty and therefore the default branch of the case structure is executed.

I've worked around it by using $DESKTOP_SESSION instead and replacing the condition with expected values like this:
---
#!/bin/sh

case "$DESKTOP_SESSION" in
gnome|KDE*|xfce) # PulseAudio is started via XDG Autostart
;;
*) /usr/bin/start-pulseaudio-x11 ;;
esac
---
This works at least for Xfce and Gnome. Do not know about KDE though since I do not use it. There's a similar issue in libcanberra-0.28-1.

Additional info:
* pulseaudio-0.9.23-1
* /etc/X11/xinit/xinitrc.d/pulseaudio


Steps to reproduce:
Start Xfce or Gnome and see that start-pulseaudio-x11 is executed twice.