The round cuts on the safety are not correct or the detent/spring is not right. There should be two positive shallow cuts with a not as deep cut between them. The click you hear/feel is the detent popping into the deeper holes as the safety moves on and off. I would remove the grip, spring, detent and safety and look for burrs on the spring hole or a bad spring on the detent. My wag is that the detent could have been installed backwards or a piece of the spring is folded up under the grip so its not as strong. The detent looks like a blunt bullet with the pointy end going into the cuts on the safety and the flat end against the spring.