Ditto to what psfred says; you can often repair the diff. in a smaller-engined car, however, by replacing the plastic spider idler gear concave spacer bushings with the upgraded metal concave bushings they now sell. You will probably want the spider idler gears as well, and you will also need a new spider idler gear shaft/pin. Oh, yeah, it's not really a DIY job, unless you have equipment to measure backlash and friction - you can do it w/o all the fancy equipment and get it close enough, however; just keep in mind that you may have to re-space the primary spider gears if the new idler bushings are too tight (measure your old spider shims and order the next 2 sizes down to be safe). Pay attention to how it comes apart, because it will need to go together the same way -- mess the assembly order up, and you'll destroy your ring/pinion gear assembly (meaning bye, bye differential).

You could also have an axle acting up (if the outer fastening bolt comes loose, or if the sealed ball joint is going bad); also the flywheel plate can do the same thing in case everything else checks out (has more of a high-pitched, tinny sound)

__________________
Don't ask me, I'm a shop-owner by default