Hi, I have just bought a 2003 S3 which has the concert / bose upgrade. The sound quality is generally good except when you have a track with really deep bass. The base box thingy in the boot gives up on the deep bass parts and makes a crackling sound. Bothe speakers in the box are working and do not appear damaged. Its almost as though it can not cope with bass at a certain level and cuts out. Perhaps it is normal. I hope this makes sense, any help would be appreciated.