Undercarriage sound sources?

Just left the mechanic's today and had the front lower ball joints and upper sway-bar arms replaced. Still making a clunking/slight knocking sound. Took right back to mechanic and drove with him to witness noise. He heard it and put it back on the lift, and looked around. But had no answer as to the cause.I suggested could it be the struts? He said no. What are we missing? Motor mounts? I trust my mechanic. And believe he would rule with a proper process of elimination. Sometimes secound opinions are priceless. What could we be missing? Thank You in advance!
Vince