I've owned my ford ranger for about 1 month and now that we have snow I've noticed that if I spin out the am getting a hard and loud thump from the rear end. I have a long steep driveway and if im not in 4 wheel drive going up it and spin a little, once i get traction it thumps real hard. does any one know what this might be? I don't know a lot but I was assuming the gears in the rear differential might be worn. If that is the problem is it expensive to fix?