Before stumbling upon this module, whenever I connected to my audio receiver via Bluetooth, I had to change the Pulseaudio sink as well as set the default output. Thankfully there is an easy fix that will do both of these when a new sink is available.

Add the following to /etc/pulse/default.pa. Or better yet, if you haven't already, create a local config for Pulse audio at ~/.config/pulse/default.pa:

.include /etc/pulse/default.pa
load-module module-switch-on-connect

Now if only I had stumbled upon this before attempting to write a custom udev rule!

Source: https://askubuntu.com/questions/158241/automatically-change-sound-input-output-device#158250