I am curious, and its probably a dumb question, but its the one in the title. If my truck is sitting idling, it will sometimes kick down to a very nice rumbling sound... Only for a few seconds though. It then seems to close back up or whatever, then just has a lot more of the whooshing sound. I like the sound of the rumble, and want to know if there is a way to keep it like that. I am assuming it has something to do with the pressure building from the turbo... But i have no clue. I honestly thought the egr delete with that valve out would make it sound nicer. It sounds just a bit deeper now... But barely noticeable.