It sounds like a popping in the exhaust
Just weeks before my grail of The Woodward Dream Cruise my 65 Mustang six cylinder has come up with a persistant popping in the exhaust. Both at idle and while running. I have never had this before. And it is bugging the fire out of me. So I will be attacking the problem this week to see if I can get a grip on it. I am suspecting fuel but could be electrical.
So far I have cleaned the carb, from the outside with no net effect. Thought it might be an exhaust manifold leak so I changed that. No net effect. Sameo Sameo. I am going to change the base gaskets on the carb and spacer to eliminate the possibility of leaks there. While I am at it I am going to clean and check out the distributor along with replacing the cap and rotor. The ignition is a Pertronix unit which has been proven flawless.
Beyond that I am looking at a rebuild of the carb as a last resort. Dunno. If you have any ideas let me know.