That doesn't sound right. It's a ferd exaggerated hypoid rear, so by design it may be louder than a corporate. It almost sounds resonant, or hollow, like it doesn't have fluid in it or tolerances are out of spec. Did you notice it getting hot? Maybe check fluid level and run it, then check heat. You should be able to rest your hand on the rear bubble for a few seconds. If you can't, you need to get a infra red gun and post the temp.