Alright I made a post about this earlier and nobody had an idea, after a week of gaining advice, I have come to this question. I have a V exhaust on my 3.6 06 w/ 30k on it. I decided to remove the resonator and ad a magnaflow x pipe. Now when the engine, and exhaust is cold, on acceleration it makes a terrible cracking sound/machine gun sound. Almost as if there is a nail bouncing around in my muffler. I took it back to the exhaust shop he walked around hit it with a rubber mallet and it was solid, i stood right there as he did it. He checked the welds, and flange bolts, and all was perfect. He could not diagnose the problem, and I was on my way again without an answer. I have spoke to a couple friends of mine whom are pretty nifty with cars, my dad, and my uncle 3 of the 4 believe that it is the hot air mixing with the cold air when the vehicle is cold causing this noise. When the vehicle is warmed up it does not make the sound. When revving the engine in neutral between 2000 & 3500 RPMS, and yes I know this is bad but this problem is driving me nuts!, but when revving in neutral the sound is a lot less than when accelerating obviously with the load of the car. Is this possible? The hot air and cold air mixing to cause this noise? Why did it not do it without the pipe? Help guys!! Im desperate!!! I will put a clip of the sound up tonight or tomorrow night.