I guess this has been covered a load of time but can't seem to find a fix for it. So here is another! Same issue as everyone knock knock when cold which will go away after the engine warms up, until Knock again going up steep hill and stronger vibration felt when flooring the gas om the free way aka high way aka interstate. Car is 2013 with just over 43,000km. Dr prius app shows good battery life. Everything on the car is stock with original parts such as spark plugs ignition coils and fuel pump. I'm going to stick a K&N air filter in soon. I've noticed something odd with the car when you open the driver door in the moring. The fuel pump runs really long compared to other cars I've owned. Other car fuel pump stop before I could even jump in but this prius C will keep running until I close the door and then some. I'm thinking maybe the knocks are linked to this symptom?