Pontiac Repair: bad noise inside car while driving, Firebird differential noise

Question
2002 Pontiac firebird, 6 cyl.  Extreme noise while driving.  Sounds like a grinding howl that's amplified from the differential, brgs., or somehting to do with the diff.?  I was told that this is normal for this make and model of car.  I guess I'm a dummy, cause I bought the car anyway.  Now, how much to fix??? I love the car, but can't stand the noise! Please give me some suggestions. Thanks

Answer
Hi David:

Well without hearing it I'd venture to say it's pinion bearing that went bad in the differential. If it has been doing it for a while It may need a complete overhaul. If it just started doing it you can get away with just bearings. Ball park I'd figure maybe $500 for just bearings to be replaced and the price goes up if it needs more. Good luck :)