Knocking is a nightmare. I hope it is something simple cos I spent a year replacing everything in a vain attempt to track it down. It was worse when cold, sounded like (if you can imagine it) someone rattling a fork in an ice cream tub. Once it was warm it only did it on the more noticeable bumps, but from cold even a stone in the road would rattle and knock from the front, just inside the engine bay in front of the driver. After replacing all the bushes, bolts, bearings, mounts, reseating suspension, the lot, it finally disppeared when the top engine mount was changed.