wierd knocking c300 at running temp.
 

started to experience this knocking the past week in my 2013 c300 4matic only ater hitting running temp.. it sounds like its coming from the driver side rear top end. the knock matches rpms. I hear it at idle and below 1000rpms. seems to completely go away while driving above speeds of 10mph. I just hit 80k and always have kept up on routine maintenance. I have the m276 engine and im running Mercedes approved m1 5w40. I know im overdue for a spark plug change. any word of thought would be appreciated.

It could be the hydraulic tensioners for the timing chain where it drives the cam shafts. My X204 does the same thing.

Here is a remove / replace video for my engine type.