Audio problem

Ok.. here´s the deal.
 
I took my cayenne S to dealer the other day cause check engine light was on, they had to replace ECU in the car.
Ok, that solved that problem, but on my way home i noticed that the sound from the sterio was not as good as when i left the car there..  there is a little continuous crackin sound in the speakers, even when the sterio is turned down to the lowest volume, also the subwhoofer dosen´t boost the sound up like before.. ????
 
I´m going CRAZY cause i love listening to my sterios LOUD!!
 
HELP!!

Is the stereo in your Cayenne stock or aftermarket? Let me know and I can help