Hmmm...I don't either, actually. I lumped "self-leveling suspension" into "electronic dampening," which is likely completely different. I looked on BMW's site to see if they could state what electronic dampening was. So I looked elsewhere. Here's what it says:

Electronic Dampening Control
Monitoring all movements of the car, an electronic control unit determines the optimum level of damper forces and adjusts the suspension within fractions of a second to different road, load and driving conditions. When setting off, applying the brakes and in maneuvers, damper forces are increased. When travelling at a constant speed they are reduced for more comfort. You can also choose a sports setting manually. This system enables you to enjoy optimum handling and comfort whatever the conditions.

I don't know that this is the actual cause of the noise, but it seems logical that it could be calibrating when a door is opened. (The electronics assume the vehicle will be driven.)

Okay, so that's my last stab at guessing this. I'm likely completely full of it--and someone who actually knows what they're talking about will speak up.

Joel