The shutter sound is different on my 5D MkII when compared to my 300D but very similar to my 40D. Also bare in mind the different sounds you get in different shutter modes eg Continuous, one shot and silent. Try each setting and listen for the difference.
As for the black mark, Gordon does make reference to a "black mark" in this viveo review....... http://www.cameralabs.com/reviews/Canon ... iew2.shtml
also go to the full review, you will find it in camera reviews on this web site.
Hope I've been of some help.