I have a 96 Audi A4 2.8L that suddenly was making a loud 'knocking' from the engine when I was pulling into my garage. I started the car the next day and still heard a loud knock, assumed a thrown rod or knocking valve. I took it to an Audi mechanic who said he put the stethescope to the block and said the sound was deep within the lower engine. Not worth tearing the engine apart to find the problem. I waited a few days and decided to take a chance on driving the car back to my house. The battery was dead, which was strange, so I had to jump the car and once up and running there was no noise. I drove it 8 miles with no noise, lack of power or smoke. I have since taken the battery out and tested, which was revealed to be dead. The question is now what was the noise and does it have anything related to a dead battery? Any thoughts?