My BMW 325 had the same problem. I think it's a problem with the differentials. It's pretty easy to fix, and the average repair shop or dealership should be able to have it done for you.
Can you identify where the noise is coming from? After I hit a pickup with my BMW, and sent it to a repairshop for repairs, there were no more noises when I made a hard turn. I only saw on the repair bill item for damaged exterior panelings and lights, so I assume that fixing this problem was easy and they just did it along with everything else.