When I open the cap the whistle stops. The gasket looked fine but I cleaned it anyway as it had an off color 'coating' of some kind on it, probably a combination of whatever contaminants are in the fuel. I suppose they could build up inside the narrow hose but I did notice a bend in the hose that may kink and not allow the fumes to pass thru. Have to figure a way to replace the hose with a new stiff one maybe.