nataliya

Hello, I drive a Mercedes C300 and recently my Audio system started messing up and I'm not sure how to fix it. What it does it it opens half way, then closes, then opens half way again and closes. It keeps doing that until I turn it off. The only thing I am able to listen to is the radio station I was on before it broke.
Any ideas why it's doing this and how do I fix something like this?
Thanks much.