Turn the wheel to the side, with a flashlight, look real close at the rubber gasket on the U joint end caps. You can stick a pry bar (or screw driver) through the yoke and pry the axle shaft, a little one way and the other. If you can see the bearings at the ends of the U joint move in the cup/gasket, ther is too much play. There is often a ring of rust dust around the bearing cap gasket, when they are bad or going bad. Any play of the cross bearing shaft, in the bearing cup and they will start to completely fail fast.
Another methode is to jack the tire off of the ground, turn the steering wheel to lock (usually right when checking the right side and left on the other side). Turn the tire, you can hear the grinding sound of a dry U-joint and often see the play at the bearing cap. Block a tire and don´t stick any body parts under a tire.
Even if this isn´t your problem, an inspection couple of times a year, may save trouble, when your on the road.
