I have had my Jazz se sport new since 2006 it has only covered 18000 miles. on the motorway I easily get 52 mpg at 70 mph. However I also get the rattling at cold which disappears when warm. I've had this checked by my usual mechanics and they have confirmed that it is piston slap. Which they do not think will get any worse. It's due to the fact that the pistons do not have extended skirts and just consist of a piston head and enough skirt to house the small end gudgeon pin.