In journalctl shows some warnings that are the result of the fact that pulseaudio is started multiple at boot and user login. After analyzing I have identified the following locations which start pulseaudio:

Systemd user service:

$ systemctl --user is-enabled pulseaudio.socket
enabled
$ systemctl --user is-enabled pulseaudio.service
enabled

XDG autostart

 ls /etc/xdg/autostart/*pulse*
 cat /etc/xdg/autostart/pulseaudio.desktop
 

XFCE session startup

 cat ~/.config/autostart/*pulse*
 

~/.config/autostart/pulseaudio.desktop. This file is created and set (hidden=true/false) by (un)checking XFCE → Session and Startup → PulseAudio at startup