I have a 1999 A4 Avant 1.8T, however since upgrading the head unit I now hear 6 beeps when I turn the ignition off and remove the key. The best way of 'describing' it is "duh do, duh do, duh do" in quick succession - Has anybody encountered this before?

Incidentally, I have fitted a Sony Head Unit and these 'beeps' are coming from the speakers. Is this something I have done during the installation of the new radio?