I have found that the combination of not enough media and too much brass has the biggest effect on the noise lvl for me.
more media and a little less brass = less noise.....
Check the instruction manual that came with it(if you still have it)It gives guide lines as to how much of what caliber brass can be added for best effect.
Question here as well, my manual says to not clean the brass for more than about 2 hours....What is everyone else doing? I usually clean a little longer than this to get the desired results.