Absolutely this would cause a knocking noise...I would replace both of the bushing on both sides to "reset" the suspension back to the same point in time, so to speak. Meaning so they are both wearing at the same rate. If you replace one, but not the other then you are stressing the weaker part to eventually break. A bad bushing could affect braking, accelerating, cornering and general ride quality, plus you might wear out your tires faster too. Its easy replacement you should be able to handle with simple hand tools and a jack. I would replace the whole arm to start fresh. I dont know if the Megan racing trailing arms are still available, but at least stock would be a good idea. Good Luck! PLease update us....