The Hatsan Squeal

"MDiver"Hi
Do you fill with hand pump?
If so, and if fitted with a quick fill, check the grub screw inside the connector.
This grub screw is a restrictor for bottle fill.
Sorry, forgot to mention, when I'm filling with a tank. I don't have any hand pump. Also just found out my bro just received a Hatsan Nova and his Nova also squeal near the top of the fill when filling with his tank.