Thanks for the ideas, guys.
I recently completely emptied the glovebox, save for the insurance papers. Driving around town lately I haven't heard the rattling, but I'm not yet convinced it's gone.
I know this may sound crazy, but do you have sunglasses or something in the sunglass holder above the rearview mirror???
It amazes me how sounds reflect around in a car off the glass and who knows what else...
I've also had the third row leather headrests rubbing against the back of the second row seats rubbing as well...
I hope you found your cure with the glove box...
This stuff can drive you crazy...