1998 Volkswagen Passat KNOCKING SOUND WHEN AIRCONDITION IS

Hey, I am new.

My Passat 1998 model 1.8T makes a knocking sound whenever the aircondition is put on especially when is it stationary. If put on and move immediately it does not make the sound but whenever it comes stationary/idle, the sound comes up. The noise is worse when reversing and could come to a halt immediately if the motion is not much. But when the sounds comes up and you put off the aircondition, the knocking sound goes off.

I have diagnosed and the diagnosis complaint about the knock sensor. When the knock sensor was changed, and the engine started, the no knock sound and after 5mins the knocking sound came up again.

Any idea what the cause could be.