Help, Exhaust noise

[Thunder87m]

I have a new 05 1800N it has about 600mi on it now. My question is that when I put my Cobra speedster straight cut pips, K&N, and Power Commander on after it warms up the exhaust sounds like an echo? When I crack the throttle it goes away for a sec. then comes back. It dosent backfire seems to run fine. What gives?
Thanks,:choppersm

[Quinnmotorsports]

did you have a program for the commander that is set for those mods?? and sometimes you will get a echo at tidea due to the amount of flow comming threw the pipes. this is normal once you get the air flowing it will stop doing that