Sure its the rear glass? I read something about a rear trim piece, maybe driver side rear window, rattling?
If not that does the glass look as if it’s sitting flush (lined up) with hatch? Maybe theres some adjusment on the catch on the hatch?
Edit* Maybe i read your post wrong... is the release button that rattles or glass?
After a month or so of trying to figure it out. I found a sea shell that my daughter found, she put it in the back passenger side wheel well compartment. Removed it and the noise went away. Or so I thought. It started back up AGAIN.
Low and behold, I lifted the window and was trying to figure it. The trim piece on the tailgate drivers side has popped lose and is hitting the window.
I thought I had looked over all the trim pieces after you had mentioned it but, I missed this one.
Now I need to figure out how to secure it. One of the plastic pieces that secures it is broken and there seems to be something holding it off, so it wont stay.
At least now I know what it is
Still drives me nuts though