Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Al, trying to diagnose noises like this is very difficult over the internet especially with something so subjective such as your issue. Some noise is unavoidable but if it is very noisey then there may be an issue - a faulty injector can cause knocking noises and this may be an issue with your vehicle so I would always recommend taking the vehicle back to your dealer for investigation.
I woul suggest asking them to keep it overnight for a cold start test when you do book it in
If you are not happy with the dealer if they say nothing is wrong then I would ask for a back to back test with a similar spec vehicle to find out for yourself if this is just a normal noise or is a problem specific to your vehicle
Let me know if you need anything else
Best regards, Paul