your axle is bad if you can wiggle the shaft up and down. there are tight clearances on half shafts race/ball bearings. the whirring sound is most likely coming from tranny...could be throw out bearing. the reason you arent getting play from the half shaft while sitting is because all the weight is on it locking it in the up or down position. if you were strong enough you could still wiggle it....but you would need to be able to pick up a car no problem.