There have been several threads about this creaking-when-turning issue--it's very common. Mine does the same thing. Some think it's the seals, some the exterior B-pillar trim (push it and you'll hear the exact same creak). If your dealer is like mine, "they all do that" is considered an acceptable response, and you'll just turn up the radio.
Sorry Kotsby, I'm with David on this. The fact so many people are having noise from movement in the door frame, regardless of which part is doing the creaking, inspires no confidence in the torsional rigidity of the car. I had a VW Passat wagon, which like the C-Max has a lot of openings and has double-sealed doors, but even after 10 years, there was never a creak, not even when traversing lumpy unpaved ground. I realize that's a higher class of car, but "not creaking like a hoopty that's been in a wreck" is a realistic expectation for ANY car you're still making new-car payments on.
No creaks on our 2013 SEL so I guess they don't all do it.