Q: differential replacement? on 2006 Land Rover Range Rover Sport

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I just had my 2006 Range Rover Sport serviced at the dealer for new brake pads (front and rear), 4 new tires and an alignment to the tune of 3K.
Now the car is making a slight whoop, whoop sound and when I had the service guy drive with me, of course it isn't anything they did but maybe it's the differential going out, WTF.

Does this sound right? What would be a reasonable cost for differential replacement?
(1) Answer
$3000 is outrageous, even for a Jaguar or very big Mercedes for the work that you had done. A 4 wheel brake job is about $1100 with new rotors, front and rear. This is right inline with the info on RepairPal. I have worked on these vehicles, so that is also what I refer to, hands on experience. Also, when I look up the work on a Professional labor guide, it is still very inline with the $1100 range.
I would find another shop ASAP. Have them evaluate the noise and go from there.