Bought my first bmw about two months ago, noticed a dry grinding sound after three or four weeks, the noise has been diagnosed as the rear diff and after some research i have found out that this is a very common problem on the 1 and 3 series. My diff is being rebuilt this week under the warranty i received with my car, this being from a reputable dealer. My car has only covered 50000 miles and i am very surprised ar the diff failing at this mileage, will probably keep it for twelve months and get rid, not impressed at all