Knocking noise under rear passenger seat behind driver. After changing out fuel gauging mechanisms and fuel pump the dealer has been told (by Audi usa) that the cause is probably a filter element in fuel tank area which clogs and does not let the tank return air to tank after being compressed when fuel is sent to engine? the vehicle has been in the shop off and on for the last 2 months. Although dealer/Audi are trying to fix the vehicle this should not happen in a 35K plus automobile. I am only lucky that I still have some warranty time left (vehicle is not yet two years old with about 35K miles! had it not been for the warranty remaining this would have been very labor intensive thus very expensive.

- Apo, AE, USA