Could you Imagine How Hard to find out knocking noise?

So let me share my another experience today on how Hard to found out the underneath noise occurred in Hyundai Genesis BH, this morning i have job card and the problem is underneath knocking if you turn the steering wheel going to right or left.
Model:  Genesis (BH)
Model year: 2009
Displacement: 3800cc
Fuel: Gasoline
mileage: 21657 km
T/A: Auto 
Trouble Condition:

• Underneath knocking noise if you turn the steering wheel going to right or left

Trouble Cause:

• Steering Gear box ,
  = drive a car at 10km/hr then make a full turn the steering wheel to right then immediate return.

Diagnosis:
= First step i make road testing to prove the noise and to analyze where is it come from.If from the right front,rear? or from left front, rear. ok i found out that the noise occurred at the front left.2ndly step i make is to check all bolts and not and retightening them all, Again i will drive the car outside.obtusely the problem still unsolved, one thing i observe while driving the steering wheel seems like a little hard to the normal steering.
I decided to test a new steering gearbox assembly.as a result the problem wasn't appear.
Trouble Repair Guide:

• Replace steering gear box assembly.