Every time I have had a mechanical fuel pump go bad I could always tell by the engine losing power under wide open throttle as soon as I hit second gear. It seems the float bowls had just enough fuel in them to get it through first gear before the pump couldn’t keep up. Let up on the go peddle and the engine would pick up again. Take it out and run it out in first gear if it noses over about the time you grab second gear you have a bad pump. I never had one make noise that I could hear over the exhaust.