When I first start my 560SL I notice sound like bellows operating. If there are bellows (or something similar) in the A/C system does anyone know what they're made of, the noise is like a dry crackle. I was wondering if this is normal or I should do something to lube the system, the A/C works well and blows hot and cold air as required. I would rather do preventative maintenance than keep replacing parts.

I am using the A/C in auto mode if that makes any difference.