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Problem with my Prosport

Ok members, I have a .177cal Prosport. I hear something moving loose inside. When I hold the rifle out in front of me with the butt in my right hand and the tip of the barrel in my left and dip the barrel down and up (we'll call it shaking for time saving/writing) it sounds like something is rolling/sliding in the area where the barrel meets the tapered area to the breach. So with the help of a good friend and member on here we tried to eliminate things as the problem one at a time. First I made sure that all screws were tight/secure. Did the up and down test again, still heard the noise. Removed the scope and shook it. No noise. Removed the action from the stock and checked the cocking lever's 2 screws (1 attaches to the comp tube and 1 attaches the cocking lever to the action/bottom of rifle. Very secure. Shook the action as described above and I still hear it. I opened the inside of the rifle. Now mind you, my Prosport is tuned by none other than our Prosport doctor Nitrocrushr. He did an AWESOME job and the spring guide and top hat were done by a man who needs no introduction, Motorhead. So anyway, I removed the guts from the rifle. I checked the spring and nothing was broken. I checked the guide and top hat, same story, nothing broken. I removed my piston, no nicks. I left the compression tube in the rifle but I did check inside it so see if there is/was any debris or if the transfer port was damaged which there was none and no damage to the transfer port. Did the "shake" test again and I still hear it I opened up the cocking lever all the way as if I were cocking the rifle and left the breach area open as if I am going to load a pellet. Did the "shake" test to try to narrow down the area of the noise. With the compression chamber pulled to the rear, the nosie was still in the area where the barrel meets the taper and the breach area. I then return the comp tube to battery, shake test and the noise is still in the area mentioned previously. So now I know its not the comp tube, its not the piston, not the spring, not the trigger housing. I thought at first that it might be the delrin washers in the piston but when I removed the piston, those washers did not move what so ever. I am wondering if it could be a fragment of a pellet possibly. If so, then how could that be? Then I looked into the barrel from the muzzle end. Wondering if a baffle or an o-ring got clipped. I could only see the o-rings and no damage was noticed to them. I shined the flashlight into the muzzle when doing that. Then I opened the breach area and shined the flashlight into the breach loading port where you load the pellet and looked down into the muzzle and only saw a shiny barrel and its rifling. Shake test again and still hear it. 

I am at a loss. I don't know what it is or how to find out. I do not want to remove the shroud because I am afraid of damaging the finish or being unable to put it back. Air Arms, I believe, has a lifetime warranty through PA (I think) but if I send it to them, they may just want to replace the rifle. Now if that happens, then I got to replace the JM spring with the oem one, replace the Motorhead guide and top hat with the oem ones along with the comp tube that came with it. I will also be giving up a Nitrocrushr lapped and polished barrel along with his tuning of the trigger. So I am at odds of going the PA route. So any and all help would be greatly appreciated as to my situation.
 
There is no space in the area you're talking about. The barrel and shroud are a close fit and are held together with glue. There is some room out past the end of the barrel and I was thinking maybe the sound could travel down the bore. I had a Pro Elite, same baffles, and it actually popped the last 2 baffles out. I think there were about 4 baffles an inch or so long, so that leaves a little room. Just can't think of any way something could be rolling around. I sold my PS years ago, but I remember the cocking handle being hollow as well, but it is open on the ends, IIRC.
 
More thoughts. Have you removed the aluminum rail from the bottom of the gun? If you have, does it still make the sound? Maybe look down the bore with a light up from the breech area. When you can see the light coming through the barrel, bump the gun lightly with your hand while watching the light. If somethings in there, it might move around enough to block the light. If you ever find what the noise is, be sure to let us know. This is a mystery for sure. If you have a bare receiver and the sound is still there, then it only leaves the shroud area. The PS barrel is only about 8" long in total and only about 5" are actually in the shroud(3" are from the breech to the front of the tapered area) and that leaves a good bit of space. The baffles look just like little cans with a hole in the center and are made of plastic.They are a press fit inside the shroud body. I'm not sure how far they go in, from the muzzle, because I don't have a PS anymore. Can't get this out of my head, maybe a loose baffle, but I don't think it would be loud enough to hear easily. Sorry for rambling on.