Mercedes: Rattle coming from cam adjuster (1000-1200rpm), harmonic vibrations, endless searches

Question
G'day,
My father owns a Merc 180C, 1999. There is a rattle coming from the cam adjuster at around 1000-1200rpm. We've had the cam adjuster solenoid replaced with no effect. When disconnected the noise stops. Endless searches on the web have not found a solution.
Any ideas? The cam adjuster is receiving 12V, 1.7Amps, stepping in at the above revs. Is this how it's supposed to work (as opposed to a continuously variable voltage)? The mechanic has checked for fault codes and line data with no apparent problems found.

Please help.
Thanks.

Answer
Heath,
What is the mileage on this engine? The cam adjuster may have ware or the chain may have slack beyond the ability of the solenoid to maintain tension on the chain through the complete speed range.
Or if the voltage is insufficient to keep the solenoid engaged completely you may be getting a flutter in the solenoid plunger.
The chain unless held tight can set up harmonic vibrations along its axis at certain rpm.
This may require replacement of the whole adjuster unit.
Good Luck,
Let us know how things go.