If you don't have an engine stethoscope here is a trick used by technicians. You take a long 3/8" extention, as long as you can get. I have a 3' extension. Put one end actually resting in your ear and place the other end around the engine listening for the point the noise is the loudest. You may not pinpoint the exact problem but it puts you in the area to investigate.

Hope this helps. Let us know what you find.

xfirepop