If possible, could you record a short video clip of the sound and upload it to YouTube or our forum? This gives us the benefit of hearing the noise "first-hand", exactly as it sounds when you hear it. Here is a link to a thread that explains how to do this, in case you aren't familiar.
It may also be helpful to identify when the sound happens (is it random, only during left turns, only when you brake, only when you go over a speedbump, etc.).