Loud Exhast Noise

For some reason my exhast becomes very loud and raspy at high rpm, or when the engine is cold and I press down harder on the gas. It's not the noise that I am concerned about though. It's the pulsing sound. Almost like the pulsing or pumping sound of Harley Davidson. I was wondering what this sound could be. I do have a CAI and a cat-back exhast, but I have never heard this sound in any other car before. Does anyone know what this could be and whether or not it is good?