Hello and welcome to JustAnswer!
Can you describe the noise you are hearing?
Is it a whine? A growl?
Has it actually been diagnosed as coming from the differential or you just know you have a noise coming from the rear of the vehicle?
It's possible that it could be coming from the differential, but it's more likely tire or bearing noise.
Take a close look at the wear pattern on your tires to make sure the tread isn't feathered or chopped. If the wear is uneven then it will cause a noise very similar to bearing noise. If you don't have any noise in the front but do in the rear then you could rotate the tires front to rear and see if the noise moves to the front of the car. If it does then you know it's from the tires.
If the tires are ok then the noise is most likely from one of the rear wheel bearings. If you notice the noise changing a little bit if you swerve side to side then that's a sign of wheel bearing noise since this changes the load applied to the bearings.
It's possible that it could be bearing noise in the differential, but it's more likely a wheel bearing making the noise. I've seen some wheel bearing failures on these, but never any differential problems.
Being all wheel drive or front wheel drive wouldn't change the price of the repair.
The wheel bearings on the rear of your car are an assembly with the hub, unlike the front bearings which are not. The rear bearing/hub assemblies run $122 and call for .9 hour of labor to replace, so not too bad.
You're welcome and good luck!