My air con has started to smell. Not really bad (though still not especially pleasant) - like pollen, or as though you're walking through a field of oilseed rape. Then it disappears after a few minutes, but may come back later. I'm not sure, but I think it also happens when the ECO button is on. Is it likely to be the obvious problem, i.e. the pollen filter needs changing, or could it be something else? Thanks.