I'd drive it carefully and see if the noise disappears once it warms up! it's supposed to be milder this weekend....

What oil do you have in the differential - did you drive far enough to get everything warmed up? Any possibility you have ice crystals in the lube from water contamination?

If you can get the car into an underground or apt bldg parking lot for a few hours, it's an easy way to warm it up and prove if this is a temperature issue or something more serious.