1998 Expy Rear End Noise

My expy has been making a grinding noise when turning to the left or right. Originally thought it was in the steering but now believe it to be coming from the differential. Tires and wheels are stock and no signs of rubbing of tires and brakes are good. Remember someone talked of bearings needing to be replaced in the rear end. Any ideas?

I have the same problem with my 99. I was told that some models have a limited slip differential. There is an additive added to the fluid that needs to be replenished. It can be purchased at Ford. Add 2-4 ounces and then turn 4 cicles to the left and 4 to the right.

I'm going to be giving this a try.