The rear tailgate rattle

This is my second Xterra, previously the S now a 2015 Pro4-x. Both of them had this annoying rattle coming form the back tailgate. The dealership claimed they took the rear panel off but couldn't find anything. I got a Lyft ride in a same model year Xterra , and guess what, it rattled too!

So has anyone else experience/been able to fix.

and/or anyone done a removal of the rear tailgate panel?

cheers

Simon