the noise seems to be affected by suspension travel as indicated at 19 and 46 second marks of the video
i'd be inclined to say you have wheel rub, since it happens as turning g-force pushes the truck sideways
and it seemed worse when the suspension went down in the turns
look at the rear axle tires to see if you see minor scuffing on the tires, or any black marks on the wheel lip paint, it won't be much
possible causes: too wide a tire, wrong offset or sloppy shackle pins allowing the rearend to move sideways
i had a 59 3800 panel that had similar problem/noise, it also had 12" tires on back with stock suspension
i also had less than 1/4" clearance between the tire and the fender lip
i ran it that way for years without a problem, mostly due to lack of suspension movement with 1 ton suspension
3800 trucks came factory without shocks for this reason, no mounts on the frame or axle
the noise reared it ugly head when going thru a squat suspension swale or cornering hard at speed