Use the carburetor idle speed screw to set a steady fast idle speed that causes the noise to happen, and disconnect spark plug wires one at a time. I'd suggest pulling the wires at the distributor cap instead of the plug- - - -less chance of getting bit by high voltage that way. If the noise stops, or makes a noticeable change when a specific cylinder is disabled, go looking for a loose connecting rod bearing or a cracked piston at that position.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!