Weird humming prob

Hehe, I know exactly what it is.  Your clue that you are using your factory head unit is what gives it away. 

You are using high level inputs on the amp,  that are hooked up to the rear speakers, right?  Well when you shut your door, the difference of air pressure moves the cones of the speakers, thereby creating a signal that your amplifier amplifies to the subwoofers which move and in turn vibrate the rear speakers even more.  You get a wierd low frequency feedback going on. 

How do you have your remote turn on hooked up?  If you can hook it up to the ignition of your vehicle, then the amplifier won't turn on until you put the key in the car.  This should take care of your problem unless you close your door with the vehicle turned on.  The other thing you can do is get the signal from the front speakers instead.  You may still get a noise from the subs when you close the doors, but it won't feed back on itself as the subs shouldn't move the front speakers like the rear speakers.  Good luck!

Steven Kephart

Adire Audio