IluvS500

Ok, the other day while waiting for my brother and his friends to get out of school I was sitting in the S (not mine) and i pressed the unlock button so they could get in, and it was quiet and i heard this weird noise for a few seconds, i pressed the headrest button for the rear, and they were already down so I heard the same noise again, same for when I did the rear shade. Is this the vacuum system working or something, I noticed when you unlock the car and lock it, it will do it.

MB AMG

Have the doors unlocked and press unlock again. You will hear a noise. That's normal isn't it?