I've only shot a few different bows, the A4 is the quietest, but far from quiet, not like a compound anyways. Think about it, most bows are around 175 to 225 fps, that's the string speed at release, slapping the stops. I've shot very heavy arrows from my A4, 675gr and it still pops. I've settled at 528 grs for reasonable trajectory. good to 31 yds -2 in
I would like to correct my above statement, the reference to 175-225 is of course common poundages of cross bows. Its the final speed of the string at the stops that create the noise, the faster the string the more noise that can be expected at the shot. And of course the force at which it hits the stops will greatly influence the noise level.