I have a mercedes 320ml and recently I've started hearing a tapping sound in the engine compartment sounding like a click or a tap. The tapping sound speeds up with the RPM of the engine and sounds like its mainly passenger side near the injectors. What could be the most likely cause?

 

Valve tap...caused by oil being too thin or old. Change the oil to approved 5W-40 Mobil 1 and it should go away. This is common on older vehicles.

 

Thx I'll try that its about due to be changed