May be a dumb question, but are you sure it's the engine? Does it do it in neutral and park the same as in drive or reverse? If not, it could be a flex plate crack or loose bolt.

 

Thanks for the suggestion. It does it in park, drive, neutral and reverse. It sounds like it's coming from right on top under the valve cover.

 

In the old days with 65 Chevy, we would take off the valve cover and press down on parts with a stick or such, finding what changed sound. A little oil to deal with. It won't bite.

Rockers can "look" OK, but sometime you have to measure. A yard stick held to your ear and moved along the cover can narrow it down. If you take off plugs one at a time it can also narrow things down, the thought being that no explosion in the cylinder makes for less noise from the moving parts.

 

Can you run it with the intake manifold off or do you have to put that back on and run it to put pressure on the moving parts? The stethoscope indicated a noise coming from cylinder 6, (which is where I was getting a misfire) but the wear on the cam and lifters was more prevalent on the odd number cylinders.

Thanks, sir.