What's with all this "search" stuff lately? Geez, we all had questions at one time or another, and we ALL asked instead of seaching, so let's play nice and just answer the man for Christ's sake....
Druid gave you the answer as to why. As far as quieting it down, an aftermarket barrel with quite a bit of porting will help some. You can also start taking it towards the low pressure side of paintball, and that will help.
Never argue with an idiot; they'll drag you down to their level and beat you with experience." ~ Anonymous