Wait, so the manual is basically a suggestion now and some guy in an AutoZone parking lot knows more than Ford engineers? That tracks, honestly, my Haynes manual says my truck should be able to carry a full sheet of plywood in the bed without issue, but that thing almost snapped in half last summer. I had a similar thing happen with an old Jeep, some guy at a gas station told me to ignore the torque spec on the oil drain plug and just go until it feels snug. He was right too, because the previous owner had stripped the pan before I got it, and the right spec was just asking for trouble. The real lesson here is that these old beaters have their own rules by now, and the factory numbers are for when everything was new and shiny. I'm just glad you found the noise, chasing a rattle for six months is enough to drive anyone to quit wrenching and just buy a new truck.