cud be any one or a combination of thse....tyre balancing, wheel bearings, long shaft coupling front and back, coupling mount bearings, axle oil change, axle bearings, axle gears, surprisingly..if windoe rubbers bad there will be a sound at high speeds
i had same problem, mechanic said axle need to change..check another place..found out long shaft couplings both brocken and tyres bad needed balancing and alignment ....did that and changed axle oil...now can hit 120 mph no sound or vibration...