I think a piece of vacuum line would work better than a long screwdriver. Seems to me with the screwdriver, touching the 'whatever', I would also get telegraphed vibration noise from other things. Using a piece of vacuum tubing held to my ear, I was better able to filter out other things' noise, and only listen locally.
Did you get an oil pressure gauge hooked up? Again, what is the oil viscosity in the crankcase? Do you have the movable intake flappers? I have heard they can make noise. Disconnecting the vacuum line & plugging it is the Dx process I have heard used.
tom