I have found the problem with the noise on cold start-up! It's called the exhaust pressure back flow or (EPBV) . It's designed to provide a faster warm-up on a cold start-up by restricting exhaust flow, this is attached in with the turbo and is like a butterfly valve. I am not a certified tech however I unplugged mine from the harness on the drivers side at the base of the turbo pedalstal. I found in doing so the noise went away and I had a lot better throttle response after driving on the highway. Its said that it could set off a mil or ses light, but I had no problem with this. I found by unplugging it , it defaulted to open throttle allowing more exhaust or air flow. I will be leaving mine unplugged. Truck is performing better with no problems!