The purge valve or Regeneration valve on the C class cars is pretty noisy. There is an updated line holding bracket that uses rubber instead of hard plastic to secure those purge lines.
This lessens the amount of ticking transmitted into the body.
It works pretty good too. The P/N # is 001 995 56 65.
The amount of these that get replaced are up to the tech, since there are more than one and some are hard to get to.
They were phased into production in 07/2001
Have fun.
Dr.D