Explorer rumble problem

[Rob1559]

My wife has a 2003 Exporer with 36,000 miles. When accellerating from a stop there is a slight rumble that lasts about 1 second that seems to come from the rear of the truck.
Any ideas what this is?

[RoyLPita]

possible rear posi clutch chatter. Pm me the Vin just to be sure your vehicle is equipped.