Generally speaking, all performance mufflers are louder than stock mufflers. Among performance mufflers some could be louder than others.
How could we tell?
If you are looking for a quiet performance muffler, here are a few clues:
1. The muffler has a smaller outlet
2. The muffler has NO sliencer
(A Twin-Loop Chamber muffler is usually quiet because of its construction).
However, if you are looking for a louder muffler, here are the features you should take a note:
1. The muffler is shorter in body length
2. The muffler has a bigger outlet
3. The muffler has a silencer installed
Take the silencer off, the muffler could get really loud.