Whenever I loose traction and spin my tires, or my rear end hops/skips around, like going down a hill, it makes a loud loud noise... it sounds like from the rear end.. it happens when I hit a big rock or stump sometimes too, it's very embarrassing! any suggestions?

Hello this is my first post as i just got an 05 outlander xt 4x4. After changing the differential oil, motor oil etc I decided to put a couple of pumps of grease in the grease certs of the u joints and found that a typical grease hose cant get in there..Is there some trick or special grease tool...