I recommend taking it to a dealer who knows the difference between a turbo and a supercharger.. jeez.. !
Yes, the clutches disengage and re-engage on the C230 Kompressor (=supercharger) at a certain RPM. In an '80s Mercedes, this would never be allowed to make a noise, but it seems anything can get through quality control these days at Mercedes.
This is not *definitely* your problem though, there may be other causes of the noise. There has definitely never been a C230 created with a turbocharger though, either petrol or diesel, the nearest I suppose being a C220 CDI Diesel.
Please confirm if the dealer really did say 'turbo'.. It would really make my day!!!
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black