I just bought a 98 JGC Laredo with the 4.0.

I hear a rubbing or light grinding noise coming out of the back end basically who whole time it's moving.

I'm not a mechanic but it does sounds like ball bearings are getting rough. I hope this is not a costly repair.

 

Check your brake calipers to see if one is dragging or the rotor is scored. Look at the axle seals to see if they are leaking, you could have an axle bearing shot. If the noise changes with power on or coasting, it could be pinion bearings. In other words, do some inspecting. It could be something simple like a bent brake dust shield.