Exhaust sound fluctuates- Input

Hey everyone, so i want some input from you all. I have a o/r h pipe and flowmaster outlaw resonance chambers and the exhaust sound seems to flux between certain rpm ranges. On mine between 2000 and 2500 rpm seems to be the loudest and right after 2500 it quiets down. So right now i am trying to figure out whether its the resoance chambers doing it or whether a set of after market cams will fix it. Please comment your exhaust setup, cams, and what rpms yours seems loudest and ill see if i can find a pattern here. Thanks