I believe that's what may be happening. It doesn't feel like a lot of gas blowing back to me, but I have pretty long arms. So the pistol is out away from me.Its possible the increase in sound is due to the slide coming back enough to let gas out before the bullet exits the can. Gas is escaping back out the ejection port. Do you have a lot of “gas” blowing back in your face? Let someone else shoot it while you stand off to the side. Sometimes its louder to the shooter then ti those standing by.