The hardest to find rattle coming from my dash turned out to be outside the cab. Look at the picture below, the yellow circle shows the spot where my rattle was coming from. The corner of the windshield wiper cowl is supposed to have a foam/rubber cushion to stop the corners from vibrating and rattling. When the foam/rubber wears out, the corner of the windshield wiper cowl taps on the outside of the upper firewall area and it sounds like the noise is coming from under the dash. I happened to find my rattle when fixing my windshield washer hoses. Once I replaced the foam piece at the corner, my rattle stopped.
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P.S. This is a shot of my truck at Moab in 2019. Had a blast! 😃