{SOUND_TYPE}: Rumble {VEHICLE_MODEL}: Audi A3 8P (Solution)

In an Audi A3 8P 2.0 TDI with CFFB engine, noticeable and difficult-to-locate knocking noises occurred between 1200 and 1400 rpm.

The roaring sound comes from the 180° bend of the air intake pipe from the air filter to the radiator grille, along with the small air box on the radiator grille. Check the airbox on the radiator grill for a secure fit (using Torx screws), inspect the vibrating surfaces of the individual components (disassemble) and degrease with acetone, then cover with thin felt strips so that nothing can rattle anymore.