Sometimes the piercing tip of the exhaust valve gets stuck in the cart when you shoot it all the way down to low pressure so the noise is the valve stem going back to it's spring rest position, nothing to be worried about. Normally if you stop shooting when you notice a significant drop in POI instead of going all the way down it won't happen. Sometimes the cart's even get stuck in the tube which can be fun.
Not exactly what I call fun. I had that happen on two different guns, and had to disassemble them to get the valve with the stuck cart out. Acutally had to hold the valve in a padded vise and twist the cart off the piercing stem with a pair of vise grip pliers. I noticed some fine mill marks on the piercing stems and stoned them smooth then polished to a mirror finish. Have not had a stuck cart since doing this.
As for loading pellets, I find that flat nose wad cutters tend to try to jam on that little screw that holds the breech to the action tube( is that the right term) round or pointed pellets seem to feed smoother, but I like the candle wax to smooth things out there, works great.
