Steering System Noise Definitions: Knock
WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
Knock is a loose-sounding rattle or vibration generated by the steering column shaft contacting other portions of the column assembly. The noise is both audible and tactile. Knock is generated driving over cobble stones or rough pavement. It is not necessary to turn the steering wheel to create this noise.