Sounds like the servo might be binding up. Try disconnecting the control rod and see if it still makes the noise. If it does, the servo might be defective. If it doesn't then manually work the control rod. It should move smoothly. If it doesn't, you need to find out what is causing the hampering the control rod's movement problem and correct it. Do you have a more experienced pilot you can have take a look at your setup and help you find where it is binding?

Hope this helps,