Hey! Is the clacking normal? With gas recording it disappears and only appears in idle mode. (no matter if the engine is warm or not the noise does not change) I have seen several YouTube videos and some have not. Some say it is normal again.. I can’t really believe that.. Be sure to change to 5w-40 soon.. maybe it will help. Listen to the video and add your mustard! Important basic data: SLK 350 R171 Built. 2004