please listen to this engine. Before and after. I fixed
The problem. The noise was a broken mount for the belt tensioner

https://youtu.be/teTYwyLGsDw before repair

https://youtu.be/u0qhTPaHo6A After tensioner repair

Older description of problem below.

I bought this car a few months ago. The engine noise has been present since i have owned it. All services are up to date. !90,000 miles on engine. Does not smoke and has excellent power. There is NO abnormal noise when over 1800 RPMS.
I rebuilt the injectors with Monark nozzles from Mercedes Source last week. The engine was smoother (not vibrating) but sounded no different. The shop that rebuilt the injectors said one injector was releasing too soon and one was too long. Three were good. I had them all rebuilt with the new monarch injectors.

Let me know your thoughts. I would be appreciative .