As with any car w/mechanical adj. valves there is noise. This is why almost no car maker uses this design(not to mention emissions). The clearance for the intake side is less than half of the exhaust, so the noise comes from the exhaust side. To adjust the valves the cam must be removed & different size shims have to be installed.
This is very labor intensive & the shims cost $5-8 each. Were you billed for shims?? M.B. has a form for the valve adjustment, the clearance has a large +- value. Setting the valves to the lower mean value(takes time) will help with valve noise, runs better too!
A lot of the engine noise on 16V engines comes from the piston clearance. These engines were designed for racing & have more piston to cylinder clearance than most engines!! So don't blame all of the noise on the valves.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH