Abstract: A secondary air injection system for reducing the hydrocarbon emissions of an internal combustion engine that is provided with an air pump supplying air to the exhaust manifold of the engine through a check valve assembly and an elastomeric hose characterized in that a baffle in the shape of a helix is located internally within the hose so as to cause the exhaust pressure waves from the engine and passing beyond the check valve assembly to impinge upon the solid compound surface of the baffle and be divided and diffused as they progress along spiraling paths so as to prevent objectionable noises being generated in the hose by the pressure waves.