Something loose sliding left-right inside Macbook Pro retina 2015

We have an early 2015 Macbook pro retina 13" and upon moving the laptop the other day I could feel and hear something sliding side to side, it feels like something solid and is towards the back where the hinge is located. I don't think it could be the battery as these are towards the front and stuck down with tape having seen various pictures. I thought it could be the screen itself but there is definitely no movement there, I am now thinking it could somehow be the hinge mechanism itself?

The noise is also more noticeable when the device is open with the screen up, not so much when closed.

All I can say is that everything works fine, including the hinge, but this noise is bugging me. I have booked an appointment but the earliest is in six days time. I was just wondering if anyone else had experienced this. The Macbook is only three months old and not had much use - my wife primarily uses it and is a teacher and it's been the summer break.