Just picked up my M6 last week and am currently getting to know it. One thing that has me curious is it seems like if I'm making multiple trips to unload the backseat of things and continually open the door with maybe 5 minutes between each opening, I hear a whining sound which I assume is the SMG pump pressurizing. However it is each time the door is opened, should the pressure bleed off that quickly or does it not hold it? Obviously it's not every time the door is opened, but if there is a few minute gap in between openings it will almost always do it. Normal?