Adjustment to door closing

[Cabrio330]

I friend of mine has a 2005 zhp convertible with steptronic. Recently we went on a scenic drive and we swapped cars so he could drive my 6-speed zhp convertible and I drove his step. At our first stop, we both noticed simultaneously that the sound of his driver door was distinctly different than mine - it almost sounded like it was slightly misaligned and the door strike (?) was hitting something too hard. He is the original owner so he is certain there has been no damage to the door; the car has never been an accident of any type. Perhaps the door has sagged a bit over time?

Anyway, neither of us could figure out how and where you would adjust the door hang to try to eliminate that sound. Anyone here have experience with this? If it is not a DIY, should he take it to a body shop, who presumably would have the most experience with door alignment, or would an independent mechanic be able to handle this?

Thanks.

[Dual]

This may help:
http://www.zhpmafia.com/forums/showthread.php?18004-How-to-fix-difficult-to-open-doors

(http://www.zhpmafia.com/forums/showthread.php?18004-How-to-fix-difficult-to-open-doors)Apparently some doors don't have the large black end cap shown in the photo.

[Cabrio330]

Thanks, I've shared this with him!