Tuner rattle is surprising because there aren't that many moving parts. Here are a couple things to try: take off the string, tighten the main mounting nut (15mm?), make sure the small "locking" screw in the back is snug, and then slightly tighten the screw in the center of the tuning key. If it's like my Schallers there is sometimes unnecessary play there. That screw is not meant to be overly tight but if it's very loose it could conceivably rattle.
Jimmy J