It sounds like the infamous differential grind. My started out at about 12k or so and progressivly got worse particularly on slow tight right hand turns. It eventually got worse to the point where I could hear it while driving 80mph on the expressway. It almost sounded like the tire was rubbing on somehting. I did take it to the dealer. The first time the stated that my break plate needed to be re adjusted. The second time i took it in I showed them the Bmw SB and they then changed the diff fluid which solved the problem. No more grinding noise.
2011.75 E92 MW/BB extended,ZCP,ZP2,ZCV, IPOD,BMW APPS, Heatedseats,6MT, Edition Black Chrome Grills & Side Gills, CF splitters, CF performance spoiler, CF mirror caps, Turner black anodized pedals, Akropovic Evolution exhaust w/CF tips, Still Undecided on tune, AFE Pro5r, AFE intake scoops, LUX H8
2009 E92 JB/Black 335 xdrive (retired)