Rear End Shake/vibration

What does it mean when your rear end all the sudden starts to shake pretty bad while in the final gear? I was on the way home last night ( the temp. was -10 degrees ) and it all the sudden started to shake badly, thought it was a tire going down, but its not. I'm gonna check the rear end gear oil tomorrow, but not sure if this is it. Was it the cold temp., or something else?

by the way, it a 95 3.2L v6 4x4

You may of tossed a wheel weight, or there is snow/ice in the rim or in the wheel-well.