I was replacing the door speakers and used the time to hunt down a couple rattles as well. I found the attached in the passenger-side door, which explained the worst of my rattles. However, I couldn't see enough of the inside of the door frame to identify from which part of the internal door assembly it came. I'm assuming it's part of the window assembly, but as the window works perfectly well I wanted to see if anyone could definitively answer. Thanks!



Electrical tape for scale.

 

That is part of the window regulator

 

Perfect, thank you. Looks like a cover and is not critical in the short term. Appreciate the fast response!