Q: Dull knocking from the front end of the car noticeable at lower speeds

Hi. My car has been making a knocking noise lately. It has gone around 170,000 miles and it had no real issues up until now. The sound is noticeable at lower speeds. Knocking seems to be coming from the driver's side area at the front end of the car. I took it to the mechanic, and he had the right front inner rod and struts replaced along with the steering system bushings. However, the dull knocking is still present when I drive over a bit bumpy surfaces and at low speeds. The mechanic didn't find anything wrong the second time I went there. I was suggested to replace the steering rack even though there are no issues with it. I was wondering if that is necessary. Do you have any idea what could be causing this noise? Am I safe to drive the car now? Thanks.