To calculate the wavebox gph is not so simple, it depends on the tank. To do so you would need to figure out how many gallons are contained in the wave and how many waves you get per hour. Basically multiply the height of the wave, the width and length of the tank in inches and multiply that by .5 as the wave is a diagonal wedge and the volume is roughly half as a result. Then, divide that by 231 to get the gallon volume of the wave. Calculate how many waves you have per minute and then multiply that by 60. Multiply the gallons in the wave by the number of waves per hour to get your gph. In general it is a very high number, usually a 180 gets near a 15,000 gph figure.
There is no way to get it absolutely silent.