When you are in a Queue to join a Group Instance you will get a Notification at the end that you can now join the Instance, you will have ~1 min after that to do so.

Problem is however that the Notification, that you can now join the Instance, has no Notification sound.

This results in people who have the HUD disabled will not be able to notice it and in general it being a lot easier to just miss.

The Group Queue Join Notification should have a notification sound, just like every other Notification.