Hey folks - I have a new 2021...about 2 months old. I notice the engine makes a knocking sound. Mainly at cold start up but still apparent later on. Never had a 4 cyl MB so not sure if this is a common sound? It sounds like as if you took two wooden dowels and hit them together. Maybe 30-40 knocks every 10 seconds?

 

Normal for Direct Injection engines. You are hearing the high pressure fuel pump which is cam driven and the associated injectors.