Radio tray

Shut down the panel first, xfce4-panel --quit
Kill the xfce4 configuration daemon, pkill xfconfd
First delete settings for the panel, rm -rf ~/.config/xfce4/panel
Clear out the settings for xfconfd, rm -rf ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml
Restart the panel, run xfce4-panel. This will respawn xfconfd automatically. Note if you need or want to restart xfconfd manually know that on my installation it was in /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd which was outside of $PATH.