Originally Posted by KRosh

If you say it is a banging sound and not a constant griding sound, my guess is the break pads wore improperly so they are warped or the rotor is warped.

Porsche uses a soft metallic break pad and it is likely the pads wore improperly over the course of the 400 miles. It is also possible that a piece of the pad is chipped.

Let me know what they tell you - I am curious as i used to be a German Car specialist (Technician)