The CCM CF barrel is not super quiet on it. It is about the same as the stock aluminum one IMO. Quietest barrel i have tried on mine is a Sanchez SM-1 barrel, it is one of their older 3pc barrel kits. It has 8 rows of porting, it is one of my favorite barrels and super quiet, and it shoots great.
I would say the quietest will be the Whoosh like has been mentioned already.