Hello together My wife’s Fox 1.2 liters 55 hp roars or knocks like a diesel when it accelerates below 2000 rpm. I know this noise from a good old beetle as an acceleration knock which can occur when the mixture ignites through the Z.Kerze before the actual ignition with a very hot engine. I think, however, with the Fox it’s some kind of roaring from the engine compartment. I heard something about an anti-drown mat in the air filter in the connection. e Problems????