1997 GMC C1500 Rumbles from below

Drive Train Axles Bearings problem
1997 GMC C1500 4 cyl Two Wheel Drive Manual

so it started only after I would come to a complete stop, I would feel a little rumble a couple seconds after the stop, and it was not coming from the engine. Now I feel it while im stopping also, and its coming from the back of the truck. I also noticed that my drive shaft that use to be loose, is tight again and it is wet under my diferrential. What do you suppose it is and what should I do?

rear wheel drive only