What is that rectangular looking thing on top of rare window? It has rubber edge and I can lift it up and stick my fingers under it. It is making this rattling noise at times while driving. Has anyone experienced this before?

 

The third brake light?

 

This is the third brake light. Don't stick your finger under it, or a gap will form and braking at night will illuminate the rear window with a nice red oval in the center of the window. Very annoying. Mine showed up after tinting. They (good shop -- no beef here) must have pried if off a little hard and a gap formed. Together with the tint (more reflective), I had this annoying light at night in my rearview mirror. Fixed by a couple layers of thin weather-stripping.