Sadly That the very first thing I tried. So, Randomly when the Cache failed to build at Shannon and i restarted it then, it started working again. This is after 3 previous flights where the sound wasn't working, but everything else was.
The airports where it didn't come back after restarting Coustal was LGA (stock), London City (Stock), Frankfurt (Stock). If it fails again I will document the steps via a screen recording and provide a video.
Update: So the notifications, like when to open doors and such now beeps, but the actual noise of the boarding and trucks are not working