That definitely sounds external, vs something going on internal to one of the powertrain compenents like tcase or tranny.
I'll bet you can figure it out with an inspection underneath. maybe one of your exhaust hanges came off the rubber and it rattling on something. also check your engine, tcase and tranny mounts.
does your parking brake work? even though you don't use it, need to rule out that the drum internals didn't fall apart in there.
ISIL and al qaeda can go F*ck themselves...