Mark:
I have a 2001 C555ES and I found that going through the "Classification by the Layer Configuration" routine for Super Audio CD + CD on page 13 of the user's manual did away with the mechanical thumping/grinding noise. Might have been coincidence, dump luck, or any combination of the two. In case you do not have the manual, here is what to do:
1. During stop mode, press MENU
2. Turn "/AMS/" to until "Layer Select" appears in the display
3. Press "/AMS/" (The current default layer appears).
4. Turn "/AMS/" to select CD or SACD, then push "/AMS/" again. (The default layer setting is SACD).
I went through this in the first place, because my unit was selecting the CD layer over the SACD layer. After I did this, the grinding noise stopped.
Worth a try. Regards, Rich