Control arm bushings/ball joints..... There are some good DIY's on YouTube. they also show why you get a knocking sound from this issue. Your passenger side control arm ball joints/ bushing issue may only be noticeable when it's stressed by potholes/rough road and not when on a lift being inspected. In any case replacing both sides is something you can do if you have fair mechanical skills. The CAB's should be replaced in pairs... I replaced my control arms at the same time, pre installing the CAB's on the control arms. If I was going through all the effort to change the CAB's I might as well to the control arms as well.....
Sent from my iPad using Tapatalk