Whenever I drive, then stop, and open the door, I hear very strange sound of motor turning off (not the engine) What could it be? It doesn't sound right. I mean an expensive car shouldn't be making this sound.

Probably a radiator fan still running to cool the engine.

AIRMATIC releasing air?

The "motor turning off sound" happens when I open the door while in Park and engine still running...

Thats the screw motors engaging the rear parking brakes your hearing I believe.

That makes sense. But should it be loud enough for me to hear? I mean I would expect to hear something like this if this was a 20 year old car, but it's a 2015...

Oh ya, its plenty loud enough, no real way to silence those solenoid motors. I kinda like the sound, you can hear the motors load up a little bit when the brakes get tight, sounds a little like one of those old prop planes starting up in those old movies I pretend I'm Humphrey Bogart when I hear that sound

Wait, you said rear. But the sound is coming from the front.

Definitely not the E brakes if it's from the front of the car. Probably you should get your car checked out, might be something wrong, sometimes the cooling fans stay on for a while after getting out of the car, but they really are not that loud and definitely sound like fans. I'm out of ideas, dunno.

Sorry for the confusion. I just took a closer listen and it is in fact coming from the rear. I owned many non Mercedes cars before and never had this sound. Is there a way to disable it?

On mine there is a noise (10 secs) coming from the back when I turn off the vehicle. Seems to be fans. Also other noises from the front at various times. IE unlocking it , security timing out , opening the trunk etc. Things seem to be always happening. The car is looking after itself. Some is antipollution, gas tank gasses etc.

Its your parking brake. You don't really want to disable it.

You can pull the handle again to release them, but it will still auto-engage to keep the car from rolling when you open the door with the engine running. Safety first.

Electronic parking brakes are becoming standard on most cars, they all are audible. One of those things you are gonna have to get used to.

The other reason it's a good thing is it will save your trans when parking on hills rather than putting all the stress through the trans you putting the stress on the rear brakes. I worried about when I got my car what if those calipers jam up I'd end up with frozen rear wheels, but it seems like that is a very rare thing. Maybe on a super high mileage car in a harsh salt environment or something.