Buzzing noise in back of car turned out to be faulty fuel pump. after several days in shop the service rep told me that there was another problem -- a "burnt" or "corroded" wire near the fuel pump and fuel tank that could be a "safety issue." that was 3 days ago. still no update from the dealership. i am wondering if others have had problems with the fuel pump on the audi s4. i'm particularly worried because exposed wires near a fuel tank sounds like a serious safety issue.