rear end question

[mustangdaren]

When it is cold out and I first drive the car I get a slight squeeling noise from the rear of the car. After I drive about 200 feet it goes away and does not return unless the car sets for several hours. I noticed today that if I slightly turn the steering wheel in either direction that I get some mild vibration from the rear of the car, kinda like when driving on a concrete bridge. If you turn hard it goes away, just feel it when the weight starts to shift. Does this sound like an axle bearing going bad or a bad pinion bearing?