So I have done everything to find this mettalic rattle. I have:
Removed the jack
Removed the jack crank
Put rubber pads on the licence plate bolts.
Lined the hatch cover with 3m sound dampening material.
Put butyl in all the retention clips on the hatch panel to stop them from moving.
Removed the spare tire.
Put tape on the hatch latch.
Rear seats up and down.
Checked every bolt for tightness.

And still it is as clear and loud as ever. Could it be inside the wiper motor? More prominent in cool weather.
Any other ideas

 

My hunch is on the rear license plate. I'd take a look at that again. Does your rear license plate have 4 holes? (2 on top and 2 on bottom) How did you put the rubber pads on the bolts? (not sure what you meant by that, did you literally put the pads on top of the bolt heads?)

For me, the rattle was that the rear license plate only had the top two screws installed. I confirmed the rattle by tapping on the rear license plate with some moderate force. I put thick rubber pads over the bottom two holes BETWEEN the car and the license plate. That got rid of the rattle for me. Alternatively, I could have put two more screws into the bottom 2 holes, but I had rubber pads lying around. The trick is that the license plate needs to be secured in place. If the rubber pads aren't thick enough and there is a gap between the plate and the rubber pads, the plate may still rattle.