I am in the process of replacing all my speakers except door(for now) see link below. The doors in most are a mini subwoofer. You can play with your eq settings(depending on stereo). The speakers in Boxsters are garbage!! (at least earlier versions). You could have very well blown a speaker as I believe the amp is hooked up to the fronts and doors or you could have your bass up too high. Did it happen before with the
same song or is this the first time you played that song?
http://www.987forum.com/forums/showthread.php?t=21452