If you’ve got a rattle coming from your heating and air conditioning system, you most likely have a problem with your air handler. All HVAC systems have ’em. It’s usually a large metal box with a blower, heating and/or cooling elements, filter racks or chambers, sound attenuators and dampeners. Air handlers usually connect to ductwork that distributes conditioned air through your home. Occasionally, they blow directly into a room with no duct work at all.