I thought my spare tire was causing this noise (the washer was upside down and it wasn't secured tightly), but I tightened it and I'm still getting this same sound. I also thought it might be the latch for the hatch, but greasing that didn't change anything. Putting the seats down made it easier to hear from the driver's seat, so it's either something with the hatch, or something in the trim or spare tire area.

Any ideas?

Two videos here: https://photos.google.com/share/AF1Q...ExQXNBVC1jaVZR

 

I'd suggest having someone else drive your car on the same roads/conditions.
Then, you can sit in the back and try pressing and releasing several trim panels/seats around the interior while the noise is present.
Once you've been able to isolate the area, you can address it accordingly (foam padding/sound deadening pads etc.).

I have a similar noise, but it's only noticeable on certain roads/conditions.
As a result, I haven't addressed it yet.

good luck!