I can’t argue with or refute anything you guys have stated because I am still on the losing end of this proposition.
Presently the seats are out of the truck for the purpose of sound insulation. I will drive it with the passenger seat out (buckets) and continue to investigate. Multiple observers have said that the sound seems to emanate from some point in the upper rear passenger side corner, as though in the B pillar.
I don’t know what could generate such a sound in that structure. Could be referred/ transmitted from another area , as you suggest. Hopefully the sound deadening treatment will make the source more localized and obvious.
