Are you saying that you don't hear this noise normally, like driving the car? Many cars make unusual drivetrain noises running (freewheeling) on a hoist with the wheels off the ground (no drivetrain, rolling resistance). You should hear all the strange sounds ALL AWD Volvos (or other AWD vehicles) make running them on a hoist, sound like everything's bad.
If you're not hearing anything normally, then you have nothing to worry about.
Un un-torqued hub (?) or axle spinning as you've mentioned will make noise, no doubt.

As for the vibration, despite what you say about balance, a high speed vibration is most likely due to improper wheel balance although I wouldn't rule out a bad tire (out of round which should be visable as you're watching it spin on a hoist) or slighly bent wheel (also obvious spinning off the ground).
Have you tryed rotating wheels front to back?