What is this part found in my door?

[Mrgbojangles]

I took my 2004 Solara into my Toyota dealership for inspection today. I also told them that we have heard something "rolling" inside the passenger's side door off and on for about two years. I had asked them to check it before but they said they found nothing. Today I insisted that they take the door off and lo and behold they found this round brass part . They said they don't know what it is but that it is NOT part of the door or window system. I suppose it is possible that someone dropped it inside the door when the window was down (although who when and why seems puzzling)

Here's the question: Do you have any idea what it might be.

http://www.youtube.com/watch?v=PeQmj2Ctqw4

I included a $1 casino chip in the video for a size reference. The part has a threaded dimple in the center and four cutouts around the circumference.

Any help will be appreciated.

[Airjer_]

is the center hole threaded?

[Mrgbojangles]

Yes, the center hole is threaded.

[Airjer_]

I think that is one of the nuts that secures the window to the regulator.