Bullboss hammer metal doing loud

[DIMART 61]

I have a bb .25 also equipped with a wolf suppressor. It’s extremely accurate. I shoot H &N Barracuda 31.86 g gives me the best performance. My problem. When I dry fire the rifle it makes a quiet wish of air, sounds great! When I shoot the rifle with a pellet in the chamber a hear a striking sound like a thud or metal to metal sound! I have a modified depringer so there is non of that ping sound. I ordered a Huma reg I will install it. Is this just what this Guns sound like? Why where there’s no pellet it sounds like I want it too! I invested some money in this thing. Thanks) any replies are appreciated   

[Thane]

My BullBoss also made a lot of hammer noise. Bored hammer face and pressed a nylon plug. Really quieted it down also made velocity more consistent.