I have never seen a bull with a hump like that but I have kept old cows that would have a hump like that trying to get one more calf and they always fall apart in the hips. I would sell him now while I had something to sell. When a  bull starts cracking and popping in the hips it will be over. I think it is a sign of age, calcium levels and wear and tear on the frame. You cant reverse all of that.