IMHA, Sounds like you may have to rebuild your regulator. Ive seen where the regulated air pressor goes up and only thing that happens is the noise goes up and shot count goes down.
Let me try and explain why,
The tranfer port is sized to allow so much air thru to the barrel. When the hammer hits the pop valve, the valve open the air race's out and up thru the transfer port. The transfer port has enuff resistance to force the air to slow down. Kind of like spreading out the charge over a longer space and time. Now your pellet fly's out the end of the barrel but there this long high press charge behind the pellet as it leaves the barrel thats not pushing on the pellet. Try and think of the pressure as a log of air that propels the pellet,(assuming regulator setting around 125bar) your log of air would have a 125 bar leading slowly tapering off to 0. If your transfer port lengthens the air log the louder sound you hearing is the air after the pellet leaves the barrel. Very much like if you where to shoot your gun with no pellet. That also why your shot count has drop. Your wasting air making noise.
Your gun's been tuned I would guess that the tuner has maximize your FPS per the regulator and transfer port size. Hence giving your gun the highest power and shot count per fill.
