I have a 2002 Alfa Romeo 156, 1.8 liter engine. Regardless of the gear it’s in, there is a somewhat loud noise. This also occurs while in Neutral and the engine is “revved”. The noise sounds a bit like a chain being pulled from behind the car. IT also sounds a bit like - imagine this - a wing nut is loose on the air-filter housing and the washer is vibrating on the threaded post.