Had first an adapter from eBay for 6.99 in my Audi A3 (8L) 1.8T 1998 installed which constantly whistling caused through the speakers. Due to the very good reviews I decided to test once this adapter here. Lo and behold, the whistle was immediately gone! Class adapter that simply plug can be used to play! (Installed with a Kenwood KDC-BT53U)