I have a 2002 A3 which I have recently bought. When the stereo is on (alpine), the rear two speakers emit a rather loud (unless you turn up the music) humming/buzzing sound, bit like an electric guitar amp kind of noise. Its really bugging me. Has anyone else had this problem? There is a factory fitted sub in the boot but its definatly not that. And it has a nokia bluetooth hands free kit installed, but I took out the speaker and mic, just need to find the rest of it so I remove it altogether.