Respond with a softer sound-common definitions
Having taught from grades K through 8th, I find that when I try to be louder than my students, THEY get LOUDER

. I can't see using louder noises as being effective. If anything, I would use softer, unusual noise makers. I have some soft chimes in my room, but I don't often use those just because I don't want to have to walk across the room over to where they are kept. I've heard of some teachers keeping those outdoor hanging garden chimes to get their students' attention, too.
Rather than make louder noises, I simply raise my hand and say in a regular, calm voice, "If you can hear me, raise your hand and wait for further directions." As soon as one or two raise their hands, I thank them and say it again. As more students raise their hands, more of them respond. Those few times when I'm not getting the response I want, I will walk over to those who are still talking, continuing to remain calm (at least outwardly!

). Walking over to talkers has always done the trick. Fortunately, I can count on one hand the times I've had to do this in all my years of teaching.
It also helps when everyone has a common understanding of how loud the group can be. I use a number system similar to one that I've seen on other sites:
Level 0-NO TALKING at all-Used during testing or individual work
Level 1-Whisper talk-I teach them what it is to whisper and what it is to talk quietly
Level 2-Partner talk-Talking quietly so only the partners hear each other
Level 3-Group talk-Talk loud enough to be heard across the room
Level 4-Too loud for the room
Level 5-Outside recess talk