What would cause a "growling" noise in the differential? on 2001 Dodge Intrepid

This noise was discovered when I was having the tires checked. There is a vibration at speeds over 35 mph. Slight, like you are travelling on a rough road. And where could I find estimates on the average cost to replace a differential?

Asked by for the 2001 Dodge Intrepid
Might just be the front drive axle or hub