knocking when i turn in the steering on 2006 Pontiac Grand Prix

What is the intermediate shaft and where is it located.

Asked by for the 2006 Pontiac Grand Prix
The the intermediate steering shaft connects the base of the steering column inside the car to the steering gear which is mounted to the front sub-frame. The intermediate steering shaft includes two universal joints which are needed because the steering column and steering gear are not in line with each other. The shaft can also lenghten and shorten slightly to allow for flex between the frame and the body.