My Wife's 330d e46 has done 184K miles but still goes great. Unfortunately there is a rumbling/whiring noise from the back end. I initially thought it was a wheel bearing so changed all four. This did not cure it so I changed the diff oil, again no improvement. I considered it could just to be tyre noise but it does not change on different surfaces. The noise becomes apparent at about 20 mph and changes with speed. It is an auto, I tried knocking it in to neutral but this doesnt affect it, nor does turning left or right. I am at a bit of a loss, do diff bearings go and make this noise?