in a vehicle with an engine , an engine air flow system for attenuating engine noise comprising : a first flow path of air intake through which a first gas flow is substantially into the engine ; a second flow path of engine exhaust in which a second gas flow is substantially out of the engine ; and at least one duct in flow contact with at least one of the first and second flow paths , wherein the duct comprises : a tubular fluid flow passage ; at least one open end connecting the tubular fluid flow passage to the at least one of the first and second flow paths ; a support structure preventing radial collapse of the duct during occurrences of a negative pressures , caused by the engine , within the duct ; and a pliant material attached to the support structure forming a gas - tight tubular duct wall for the tubular fluid flow passage , wherein the pliant material forms , on the support structure , a series of loosely pliant panels that freely move radially outwardly and inwardly , wherein during engine operation sound generating vibrations of air into one of the first and second flow passages cause the loosely pliant panels to vibrate in a direction radial with respect to the duct , wherein a detectable level of audible sound radiated by the engine is attenuated by the duct .