V6, AWD, cold weather, rear end noise

[IlliniVue]

I recently purchased an '05 V6 AWD Vue and love it so far. However, in the last few days, when the temp is below 25, there is a loud "humming" noise coming from the rear (i think).

I really don't notice it until around 55-60 mph. It get alot louder when I give it gas at this speed. It has a deep resonating sound, but I don't think it is exhaust or engine related, because it is not effected by RPM, only speed.

The strange part is that it goes away after maybe 20 minutes. The car has reaced full running temp before this.

Any ideas? I would think a tranny or wheel bearing problem wouldn't go away, and wouldn't just show up since it got cold. Rear diff? Torque converter?
Anyone had a similiar problem?
Not sure if this belongs in Vue general or Vue tech?
Thanks.

[IMkenNY]

Sounds like the RDM (rear drive module) is locking in the cold . It should only be locking when the front wheels slip.

Check your tire pressures, very low front tires with normal back tires might just be able to lock a sensitive RDM.