Engine Knocking problem on Lexus Cygnus

Hi gyz, this is a Lexus Cygnus 2003/2004, having engine knocking issue, no check engine lamp, no fault codes. We have already done a continuity check for every relative wiring to ecu. And also the engine has no mechanical problem.
Its been 4 weeks the car is in our workshop and the car owner is not happy with us, so I'm seeking for help..

I suspect something is lost in translation here. !

Is this a Diesel or Benzine

Well it's Benzine

Lets be clear on this, you have a knocking noise, there are no mechanical defects and no fault codes (on your scanner).

Is it knocking or pinking ?

Does it do it stood still or when driving, going over bumps ??? (I have driven on Indian roads - Bangladeshi roads will be the same)