The same thing was occurring with my 06 4.8is. I took it to the dealer and they replaced the steering rack. Initially, per BMW bulletin they are suppose to try the grease method. If that does not resolve the issue, then they have to replace the steering rack. Shortly after that I had the dealership pretty much replaced the front end suspension. First, the air ride module went bad then everything else follow suit. They replaced both front air bags, control arms and struts. In addition, they also rebalanced my wheels at no charge. Now, the x drives like a dream. The steering wheel is light and responsive. Thank you for warranty/cpo. However, since my last service the tire monitor light keep on coming on. I spoke with my SA and he said I may need to have the sensors replaced. I personally spoke with the dealership shop manager, the grease method is really only a temporary solution; the sound will more than likely return. Good luck to all.