Topic: A piece of something (plastic?) rattling around inside

I bought a used Vita (UK OLED 3G model) two weeks ago.

I've used it every day and it all appears to work fine.

However, there's a small piece of plastic or something that rattles around inside.

It's not the buttons etc. rattling, it's an actual loose piece.

I think the left shoulder button may be missing some of my presses but I would need to test that further.

Any ideas what it could be? Was hoping it's perhaps a 'common' problem.