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Hello my name is ***** ***** best way is to jack up the rear of the vehicle and place on jack stands and run the driveline and listen with a stethoscope. Have you tried this?
I would just placed the stethoscope on the rear diff, the carrier bearings on the driveshaft to start. Also if the noise can'r be duplicated then you would mostly be looking for a wind related noise, check all parts of the body for loose attaching points, check the roof for loose panels or vents, ac ect.