[XthreeMist]

I have a '07 X3 M-sport automatic.
There is this rattling noise (like if you put some pennies in a dryer) from under the car, not in the engine bay. It happens when the car is on an incline (uphill) in gear or in park or in neutral or when taking off on level ground, when the car is facing downhill the noise is gone. The drives fine , no problems driving just a crazy rattling noise. If I drive in reverse then stop quickly it rattles again. It doesn't matter if the car is cold or warmed-up.
Any ideas what could cause this ?
Thanks