I think I know the sound that you are talking about and what the dealer is telling you about the grease. The axle stub that the dealer is talking about is the CV shaft stub and the noise that you are hearing is coming from the bushing that supports and allows it to freewheel, rotate etc. I do know that there is something that the dealer can do to eliminate this bushing, by installing needle bearings in it's place, and that is what might cost you about $1K to repair. Over time, the needle bearing will eventually go south. I would stay with the bushings, personally. To get to these bushings, you must remove the calipers, the rotors and hubs and also remove the CV shafts. Once the CV shafts are removed, you can see the brass or bronze bushing. Just clean it up pretty good and put in plenty of grease of your choice and reassemble. That should take care of the noise. It is more of a time consuming repair, but it is well worth it. I had the same issues and once I pulled my CV shafts to replace the boots, I greased them up pretty good and haven't had the noise since. HTH