Another thread on the DE forum, I put a post with a link to here, keep an eye on it, maybe there is some useful info we can share to get to the bottom of it. Posted in English for now, can post in German when I have time tomorrow.
http://www.cx5-forum.de/f11/motorgeraeusch-beim-fl-175-ps-diesel-5024.html
http://www.cx5-forum.de/f11/motorgeraeusch-beim-fl-175-ps-diesel-5024.html