Hey guys, my C63 2017 got around 30k KM, lately I have noticed a slight constant ticking noise coming from the engine located right above the left front tire. The sound is not very loud but loud enough to notice it and it sounds that something is not quite right. when idle i can hear the noise clear but when reving the sound completely disappears then comes back when idle within 5-10 seconds. The sound does not increase or decrease, its there when idle only. currently my car is at the work shop since 3 days now and still waiting on the diagnose from them, anyone have any idea or experience before? on a side now, 5 days ago i had a car msg that says please add 1 liter of oil after refueling once then never showed again. think it might cause that? The work shop still did not reply to me with the cause.

UPDATE: got a call from the work shop, said I have a faulty EGR valve that needs replacement, they say it is the reason of the sound.