I found this part is the bottom of my door on my 2000 convertible. I believe it is a rattle bumber as it is hard rubber. Anyone knows where is goes? It is about a inch long.

 

Buffer for the window to keep it from rattling. Recent thread here:

https://www.jaguarforums.com/forum/x...unking-222291/

 

+1 crbass,

It’s located at the top of the window guide runner. Hope you have small hands to work inside the door gap, and don’t forget to pull window fuse, or disconnect battery, when your hands are inside the door. It’ll save your fingers in case the window comes down.

The buffer probably bumped loose as your window is travelling too far up. Maybe worth also checking the central bolt for setting the window upper limit.