Take a stick (piece of old broom handle works good) about 2-3 feet long and put one end on the valve covers and around the intake close to the head and put the other end/side of the handle up against your ear and move around and see if you can determine exactly where it's coming from.
A 3 foot piece of garden hose using the same method and move it around the exhaust manifold/headers at the head to see if it's an exhaust leak.
These two things might help you isolate/find the problem.