Hello,
I have a 2019 A6 (C8) avant with the 40tdi engine. My car does a irritating humming/buzzing sound which at first i thought to be from an unbalanced AC fan but soon discovered its not as i turned the AC off, the humming persisted. I had also noted that this noise changes in tone when slightly pressing the accelerator, so it is connected to fuel supply to the engine. I have recently discovered its source when I began using the start-stop function (which i did not used), as when the engine is stopped as i stop in traffic, the noise can be clearly heard (without beeing masked by engine noise) for 1-2 secs and then it stops to reappear again as soon as engine starts. It is clearly a pump noise and it is located under the passenger seat (my car is LHD).
before this A6 I had a Q5 and the fuel filter was located under the passenger seat but had no pump. Maybe Audi moved the primary pump to this location or set a new pump on the fuel circuit, as there is also one pump on the tank (I car hear that too). I could not find any service manual or diagrams for this car, so I cannot tell for sure.
I did not take the car to the dealer but i am planning on do it soon as this noise drives me mad.
