The 210 chassis has been plagued by a variety of steering issues. As previously posted, check the P/S fluid level and front end components first. If all is good, MB has issued DTB's concerning three separate steering noise issues, depending on your cars' VIN. They are as follows. 1. An updated pressure hose. 2. A modified sealing boot between the firewall and steering shaft. 3. Replacement of the radial shaft seal inside the control head of the steering rack. They're all inexpensive repairs if you DIY, but replacing the radial seal requires some rack disassembly.

Numbers 2 and 3 make nearly identical noises, but the way to differentiate between them is easy. You say that the noise occurs when turning the steering wheel back and forth? If the noise is present only when the engine is running, the radial seal is the problem. If the noise occurs with the engine off, it's the boot at the firewall. Let us know how you make out.