Hi,
You haven't given much detail but if you have the car up on a jack when you are rattling the wheel it could be
1/ Wheel bearing, checked by gripping the wheel at top and bottom and rocking it (gently! you're on jacks). If you rock it side to side it moves the steering and can confuse.
2/ Track rod end, the swivel bearing that attaches to the rear of the wheel hub and is the connection between the steering rack and the wheel.
3/ Shock absorber, attachment at the top can give a knocking noise if it is loose. You will also notice this if you go over a bump whilst driving as it unloads the wheel.
This steering rack is the least likely but is still an option.
Cheers
westcountry, October 2013
