That's a tough one... Sounds like something with your regulator/2nd air chamber might be out of place.
What I meant to ask was "Is your bottle filled to 200 or more bar?" If it's not, that might be part of the problem.
Is this one of the raffle wins from AoA? Have you called your retailer about it? If not, do that right away and see what they have to say. They'll probably want it back to repair it for you.
I'm shooting from the hip here... The only time I hear a hissing sound is when I bleed out the 2nd air chamber for reg adjustment. It takes 3-5 second but it comes out where the bottle screws on, not the silver piece you have circled. So, use caution if you try what I'm suggesting! If your out of your comfort zone then stop and send it back.
Next time you put the bottle on, be ready to fill it. Make sure the rifle is not loaded and then cock the rifle (as if to fire) then screw the bottle on slowly until it starts to tighten. Then screw it on quickly. You'll see the bottle gauge rise to whatever pressure is in the bottle. Normally, I would screw the bottle on slowly to let everything take on the air pressure easier. I'm hoping that by screwing it on quickly you might be able to jar whatever is out of place back into place.
If your bottle is less than 200, try filling it to past 200. Take it off and try the same thing again. You'll have to move quickly to do this while leaking. Don't forget to bleed your fill line and wear safety glasses just in case! Good luck!
Tom
