Is a rifle with a muzzle break normally quite a lot louder than it's standard counterpart without a muzzle break?

Sort of.  The brake directs the gasses outward at a different angle than a plain muzzle.  This makes the rifle seem much louder to you and especially anyone to either side of you.

Hell yea!

oh man, if your standing beside one it's easily twice as loud.  

some of these shooting schools will make all the "break guy's" stand on the far end of a line.  i was shooting a breaked AR-10 "on the line" and another guy has a SR-25  between us was a guy with a plain barrel.  they had to move him because we were ringing his bell when we fired as he was getting disoriented from the constant muzzle blast.  he was wearing plugs and muffs and they didn't work as the shock waves will permeate the skull and overload the inner ear from the inside.