I have to agree with rxsteven on one thing........I would check the axle retaining clip especially if it is only one side that moves.....if both sides move then you may have a third member problem that needs to be diagnosed by a shop....which like timber74wolf said is probably a good idea any way then atleast you know what you are dealing with

 

Had it up on my buddys lift doing the brakes, its not the wheel bearings. He put a scope on the diff. and it sounds like its inside. Took off cover but couldnt really see anything. He didnt want tear into it never having done it before. I have an AMCO trany place near by maybe they will take a look for free.