I had my '06 into the dealer yesterday for a couple of things. I asked them to check a little noise from the rear end. Only happens around 40 mph, when coasting. My friend who is a tech there said I shouldn't worry about it right now, it's not that bad and he could potentially make it worse if he tried to fix.
He is capable of setting up rear ends, his concern is that right now it is minor and isolated to a specific range (really have to listen for it). His concern is that the range might move or become louder. Bottom line is that it is a 4:56 gear, a little noise is to be expected in my opinion. If it get worse, I have it documented that I noticed it early (I've only had it for 3 months now).