CCI CBLong are the quietest in my opinion, but if you fire them from a handgun, they're still loud. Like a big firecracker.
From a rifle, the noise goes down dramatically.
By the way, I was wondering if there was any powder in those CB cartridges...? I've heard that the bullet is only propelled by the primer, and since bullet pullers are not rimfire friendly, I can't really check it out...