Originally posted by ricerokets4life
yeh, ive been holding off on the repair cuz im getting the feeling my mechanic is ripping me off (still less than dealership though). he says ~$500 for labor to replace the entire belt tensioner assembly. i checked on various forums for some DIY instructions but to no avail.

maybe its because of a faulty shock? how do you tell if its the shock and not the tensioner itself?
The shock is on the earlier models but not sure if it is on your year or not. Anyway, get a flash light and check down there. Mine was pretty tucked away. To see if it is the shock (once you find it, and assuming you have one) pry a breaker bar or long screwdriver against it with the car running.( Be careful while you are doing this, you don't want any accidents.) Lean on the shock and if the sound goes away that's it.

Do a search on http://www.mercedesshop.com/shopforum/index.php3?s=

and see if you can get an answer from a tech there. It's tough to believe the tensioner is shot at 6 yrs old.

Keep us posted.

Edit: 500 for labor seems pretty high to me. Unless there is something totally different about the tensioner on a V-6 compared to an I-6.