I have a question reguarding the flap that closes until the engine warms up in the turbo. I installed the MBRP 4" down pipe back exhaust last week, when I first start the truck it is noticeable when the flap closes, when the engine warms up you can also tell when the flap opens, however when you shut the truck off (even at normal operating temp) and restart it you can hear that the flap is closed, even while driving it sometimes is closed until you stop at a traffic light you can hear the tone change, does this sound like normal operation? any help or suggestions would be appreciated.

There is no flap. There are vanes that directs exhaust on the turbines. The close during cold starts... direct 95-100% of the exhaust onto the turbine, this is where you hear the hissing noise. As for doing it at normal temps also. Thats normal. Mine hiss's all the time, but I think that has somthing to do with EFI LIVE:D

Mine will do it at startup and sometimes down the road at a red light 5 min. later, I wouldn't worry about it.

thanks fellas