It happened about a week already. whenever I get in the car close the door and the tailgate window pop open. Why is that? Is it because I lowered the vehicle and it happen. I checked the trunk, battery compartment and no water leak found. Anyone can help? Many thanks!

 

Many, myself included, had the rear glass micro switch go bad. Usually from water ingress. https://5series.net/forums/e61-touri...ch-e61-121216/

 

Yep it is without a doubt the switch. Fortunately you don't need to put the stock suspension back in to fix it