My fuel pump was making some strange noise lately, so i decided to lower the tank to have a look. At first sight nothing abnormal, only when removing the pump assy lock nut, that the pump assy didnīt come up a bit by itself, as mentioned by the manual. There is a spring in the pump assy head, which should keep some pressure on the unit to keep it fixed on the tank bottom. Took the whole fuel pump assy apart (and yes, you can change the pump separately. Mine has a pump from Bosch P/N 0-560-453-431). The spring in the assy head was ok, only the O-ring between the head and pump housing prevented the movement of the housing, probably preventing the pump seating firmly on the tank bottom and causing the noise. There where some shafing marks on the aluminum pump assy housing, probably caused by the same play. After cleaning the assy and lubrication of the seal, the assy was moving normally again.
After this no more strange noises coming from the pump.