Yashica FR-I - unknown Part loose inside the body

The FR-I is my go-to Yashica. Maybe somebody does have a clue...it was never fallen down, or anything, since decades. I got a craze of mind, i put it up like 2 weeks ago into hands, wanted to check the battery status...when suddenly, i heard a thin metal sound inside my FR-I...it's there, something i dont know about, what could became loose, and fallen as moving part inside the FR-I body? I am confused. :-( I handle my gear with most care, always.

Update: It sounds like a very small & light part, perhaps just like a thin, flat metal ring or something like that?

Greetings.