I have a 2002 A4 1.8T Quattro. I have a vibrating, humming noise coming from the rear of the car. I replaced the fuel pump, and the noise was still there. I went to the other side of the car and felt the vibration and heard the noise come directly from the sending unit...specifically from the fuel line that feeds into the sending unit. I removed the line that feeds the sending unit and no more noise. Once I put it back on, noise. I pulled the sending unit out and removed the line that goes out of the sending unit and it had a noise. After this diagnosis, I believed the problem was the sending unit, so I replaced it but it is still making a noise. I am now lost. The only thing I can think of is that it is the actual line that goes from the fuel pump to the sending unit. Can anybody help? I spent $400 on parts already and don't want to make another mistake. If it is the fuel line, does anybody have an idea of how to replace it? Please help.