if its just a slight rubbing noise, its probably the brake pads rubbing on the rotor. that is normal. when you release the brake lever, the pistons retract, just enough, to take pressure off of the pads/rotor. but they can't retract any further than the width of the rotor itself. unless the rotor is slightly out of round and the high spot pushes the pistons back further into the bore.
I understand the concept of reality, but find it too confining for a way of life.