Here is a trick for improving the sound quality on all C4 coupe owners with the Bose system. Remove the rear speakers. You will find enough space to hide a football. These cavities pick up all the road noise from your rear tires and transmits it through your speakers. Pick up some dense sound deadening material and do an inside wrap to the speaker cavity. Put the speakers back in and listen to the improvement. They won't sound as tinny and there will be less road noise too!