I found it. Perseverance pays off. It's odd, because as I was driving around, I was hammer and pushing on everything I could think of on the dash. Nothing stopped it. I grab the mirror to adjust it and the rattle stopped. I messed around with the mirror, trying everything to make it go away and nothing worked except touching the mirror. I pulled into my garage and put paper in every crack I could find on the mirror. Test drove it up and down my street four or five times. Still no luck stopping the rattle. Back in my garage, I was close to ripping the mirror off and I found the wiring for the electronics in the back of the mirror was not fully seated. Snapped it into place and voila, no more rattle.