Sorry to bump a zombie thread, but this thread lead me to discover the cause of my rattle, so I wanted to add.
I had a particularly loud buzz that was persistent all the time, no matter the speed or road surface. Sounded 100% like the rear hatch, so I took all the panels off that surround the rear glass, and I used felt tape (1" wide x 1mm thick) everywhere there was plastic-on-metal contact. Much to my dismay, that didn't solve it.
It really sounded like it was the rear glass buzzing, and I discovered that while stopped, I could tap/knock on the inside of the rear glass to make the buzz happen. Sure enough, pressing on the headliner solved the buzz.
Pulling the headliner down in the back is really not as bad a job as I thought. I just popped the top two tabs on the plastic panels surrounding the tiny rear side window, and that gave enough clearance to get a screwdriver in and pop off the clips pictured. The protruding end of the male clip actually sits on that really wide flat base which is glued to the headliner board, but the clip actually has quite a bit of play since its held on by a type of rail system. I used felt tape to stop the clip from sliding in its rail, and I then used a square of felt on the metal roof where the hole is also. Cut a square, fold in half, and cut the edge off to make a hole the shape of the clip. Did this to all four clips on my headliner, and its definitely seemed to solve my issue so far.
