i recently changed my oil on my car and found that when i start it it makes a intermident knocking noise, its not the injectors it sounds like valves. i used oem filter and mobil 1 10w 30 just like the factory calls for. its about 80 degrees in the mourning, so cold starts are out of the question. if i let my car sit for a couple of hours the engine is still a little warm and it still does it. this noise goes away a after minute or so of idling. My car has a mbc set to 21 psi and a aem intake with no tune. is something wrong with engine.