My X5 made noise in the front when I let off of the gas and coasted. The issue was a worn front differential. When the car is under load, there was no noise at all, but when the throttle is reduced and the load shifts on the pinion gear, the noise would come on loudly.

I see no reason why one would have to use a dealership part when replacing the wheel bearing(s). The shop will use a dealer part because if there is an issue down the road, he's going to have warranty considerations. It's worth it to him to sell you an OE part because 1.) you pay for it, and 2.) he doesn't face the prospect of doing the job again.