This Video shows you the sound of piston slap on a Subaru Impreza car engine. As a Subaru car engine gets older, the sides of the Pistons can slap against the cylinder walls. This is called piston slap. It sounds terrible, but a car can go tens of thousands of miles with piston slap. If your car sounds like this, don’t panic. It is normal on older Subaru engines. Piston slap usually gets quieter as the engine warms up, and it’s only really loud when the engine is cold. That’s how you can differentiate it from the sound of a bad connecting rod bearing. If your Subaru engine is making this sound, keep driving it and you’ll probably be fine. You can fix it by replacing the Pistons, but it will come back again eventually. It is mostly harmless. The engine in this car is a 2005 2.5 Liter Subaru FJ 25 engine.