2012 RXP-X 260 Exhaust Note

[RXP X 260]

Hey everyone. I recently noticed when flushing out my machines that the exhaust note has changed on my RXP-X 260. In the past when you throttle up while flushing out the exhaust...if you paused and held between 3500 and 5000'ish RPM's the exhaust note would change and really make a roar/rattle. My 2013 GTR 215 does the same thing, so I figured it's normal. But recently the RXP-X quit making this roaring noise at those RPM's...it just maintains a fairly flat note all the way to make RPM. Any body know why the exhaust note would all of a sudden change like this? Symptom of some other problem I haven't noticed yet? Thanks!