Finally got it to the dealer... and this is common noise in these vehicles. The service manager and lead technician, and I, all drove ours and a new one from the lot on the same gravel... both equally as loud at 10-15 mph. I guess it is more sensitive to some than others, but there is nothing they can do about it. About the only option is to spray the wheel liners, dampen the rear walls and bed, and maybe get the headliner kit. Fox Shocks said their shocks would probably help some, but it would not be tremendous as lower speeds like we drive on gravel/dirt roads.
