1999 Jeep Grand Cherokee

My rear passenger wheel always makes a horrible banging sound everytime I hit a bump. All the other wheels seem to do just fine, but it as if there isnt any give to cushion the blow on this wheel. A mechanic told me everything was fine with the shocks and that he even tightened the spare tire as it sounds as if the is something rattling around in there too. Any thoughts? Have others had the same problem with this make /model?