There are a number of methods to track down engine noises however. The quickest and dirtiest way is to use a piece of scrap hose like a stethoscope. Hold one end up to your ear, use the other end to place around the engine and listen for the noise to get louder. Or, you can actually buy an automotive stethoscope like so: La-Z-Link. There are other options too, such as using a long screw driver. Check this video for more info: La-Z-Link