Did you read down the page? Except for the location, sounds like the e-box fan. Sometimes sounds are hard to pinpoint.
http://www.benzworld.org/forums/forums/thread-view.asp?tid=1200386&mid=1410678&fid=29#M1410678
http://www.benzworld.org/forums/forums/thread-view.asp?tid=1200386&mid=1410678&fid=29#M1410678