It was the fork lock. I've been looking for this rattle forever. Checked everything but the fork lock. You pry the aluminum decal off with a screwdriver (it's glued on) and behind it is the "face nut". The face nut takes a special tool to tighten it per the manual, but a pair of needle nose pliers works. Lefty tighty, righty loosey on this one.
I remember a couple other guys looking for a mystery rattle coming from the front end so maybe this will help.