I picked up an 09 wrx sedan with 53XXX miles on it 3 weeks ago. This morning i started the car and i herd a faint knocking sound coming from the engine. i did a lot of research online before buying this car because of all the engine failures, and i made sure the it had a build date past 09/08. Its build was 11/08 and i did not see any issues with other cars with a similar VIN#. Later in the day i started the car again to listen closer to the sound. the more i listen the more it sounds like a knock (it seemed to get louder as well). Is there another issue that makes a knocking sound in these cars that i dont know about or is it time to look into a new engine.