Recieved my Mavic on 12-9.  Upon opening it I heard what sounded like a piece of plast rattling around inside, I could not shake it out, and eventually convinced myself that the noise must be normal (I know -wishful thinking).  I have flown a few times and the craft performed amazingly well. Infact I got too confident and broke a prop by flying to close to a plastic drum. Lesson learned, Tripod mode when doing close up shots indoors. Anyway the Mavic flew fine after that.  Today after playing with the simulator, when I put the gimbal clamp back on the plastic fell out. I think it may just be a mold piece or some other insignificant part.  I am including some photos of the part to see if anyone can identify if its just a piece that didnt get cleaned out at the factory.  Other than that the Mavic flys like a dream.  I could not be happier with it performance and when it arrived it was clean, no factory dust or anything that would make me question the quality workmanship that Im sure goes into putting these together.

Probably someone brought their kid to work. He stuck it in one on the production line xd I'm totally happy with mine too. The camera is pretty sick at 12 mp. I wish could fly it for a 360 shot but rain!

Looks to me like one of the inner tabs that snap on to hold the top and bottom halves of the body together.
Don't want to scare you but check if the body halves are loose, have play somewhere, if not keep on flying.

Thats the flux capacitor.........

I've had those break off and rattle around inside almost every phantom 3 and 4 I've owned. I was hoping it wouldn't happen again on the mavic. Oh well.....

Thank you for your feedback. I'll help to report this.