[rdorman]

Get a stethoscope and narrow it done! I thought I had a valve train problem because a noise that sounded like a knock coming from that area. I got the stethoscope (after trying the screwdriver) and found the valve train to be purring along just fine. Turns out it was a exhaust least between the header and the head. Without the stethoscope, I would have wasted a lot of time and energy. Besides, they are only about $20.
Rick