When I start my 02 C320, I get this knocking noise (in a rhythm)behind the radio. It sort of sounds like someone tapping plastic with their finger. It sounds to me like a vent or something is trying to open but is stuck. It does this for about 30 seconds or so then stops.

 

I get a similar noise coming from the rear. I think this problem is common on a lot of the C-classes.

 

I am experiencing that same problem from the back end. Its driving me nuts and I can't seem to duplicate the noise for the dealer.

 

I think Sanf (a member here) or someone else took it to his dealer to get it fixed. They took the back wheel off and checked the area. My sound i think is coming from the right rear tire area It only comes for like 15 seconds at Stoplights and then turns off. I don't think it can be fixed.

 

I believe that's the stepper motor linkage issue. Mine has been doing it since i got the car last year and i've just been ignoring it. It goes away after the first few secs.

 

That's funny....mine does it too for approx. 15 sec and it only happens at redlights or whenever I'm at idle. I describe the sound as if your tapping your finger on your desk lightly w/out the use of your fingernail. Try it......taht's what it sounds like. haha

 

I have it too, its doesnt bother me...this was one of the first things I learned about as a MBWorld member..

 

yea man. there's nothing they can do. the last thing SA told me was "newer C, E, CLS...they are all making the same noise coming from the right rear area and there isn't a thing to fix it"

get into a habbit of throwing your gear to N at stop lights. that will take care of it.