Clunk/knocking noise in 2000 LS400

Have had all struts replaced two weeks ago. What else might be causing this noise problem, which occurs at any speed over certain bumps and dips; getting more frequent. Feel a vibration/slight shaking in steering wheel/column when clunk/knock noise occurs. Feels like it comes from either front wheel through the steering column/wheel. So far, three good mechanics are puzzled. Any suggestions/answers gratefully appreciated.