So Ive replaced my battery and alternator on my 04 A4 1.8T earlier today, it started up well and drove nicely up until this evening...humming sound began from the rear bottom of my car, then the electrical failure began to take its toll, luckily I made it home. Ive visually checked the wiring and connections and all seems well, anyone have any ideas and/or suggestions, thanks a lot, guys/girls.