Hi, is this a noise you are hearing when turning the wheel or when rolling?
If you can create the noise standing still I'd have a look at the power steering fluid level.
The power steering reservoir is at the front of the motor below the left air cleaner air intake hose. It will help if you remove the hose to check the fluid level.
If you only get the noise when rolling I'd suspect a brake pad is dragging. If that is the case it will usually change sounds when applying the brakes.
Let me know if you have any questions.
The noise is only when the wheel is turned. The fluid seems to be down a little. Do I have to go to the dealer to get a specific fluid or can I just get some at Auto Zone?
You should purchase the Mercedes fluid from the dealer. I don't think Auto Zone is going to carry the Mercedes fluid.