I see the front of the picatinney rail is right over the chamber. If it is aluminum that could be giving off the ping. Just a wild guess but seems rational. If they make steel rings I would try them. Worth a shot for very little money. Did you notice it get muffled after the scope was attached. A easy test is take the scope off and shoot it. If it gets louder then there is the culprit. It should go right back to zero since it's rail.