Mine sounds like it's coming from the upper part of the door panel. Also hear a rattle coming from the seat belt holder on the pillar.

 

Mine is rock-solid and has no wiggle/slop to it. I did try removing it just in case, and no difference was made. I think maybe it's the door I'm hearing.

 

The rattle could actually be coming from inside the passenger seat, I have one that comes when it's really cold from the passenger seat, never bothered to track down exactly from where because it sounds like it's literally inside the seat itself and doesn't even happen that often

 

You might be onto something with that.

 

It could be the mounting of the seat to the tracks itself, or possibly the seat back has something coming loose that won't be apparent if someone is sitting in it

 

Maybe it IS in the seat then.

This is going to sound weird but I found a very noisy gel pen in my glovebox. If i shake the pen the end cap almost makes the same noise as the rattle. It's a soft noise and amazing how it could echo so much while driving in the car, but who knows, road vibrations can do amazingly strong things. Anyways, I tucked the pen under my butt for the whole ride home and I didn't hear the same rattle. I heard a few other small rattles but not the prominent one. Now I really wonder if it was the pen. I've since removed the pen out of my car and will see how long this no-rattle lasts. Thank god for the 4 year warranty. This stuff takes time.

 

my guess is it could be the fans under the passenger seat because when I have someone sitting it no noise but when there's no one I can hear it rattling.