Most people are not aware the
Most people are not aware the knock is not coming from the engine. When small amounts of coolant are in the cylinder on start up the misfire causes the hybrid torsion clutch to rattle super loud. I have changed 2 prius head gaskets for #2 cylinder coolant issues. When turning the crank by hand rock it back and forth and listen to the hybrid drive it knocks allot. Any cylinder misfire will sound like the engine is about to explode but is actually just the drive making a loud noise.