I have a 2007 lbz duramax. 120k miles. Truck has stock intake, egr, exhaust, etc. No tuning. I have a problem with extremely loud turbo whistle. It wasn't like this when I got the truck. It has gotten progressively worse overtime. It normally sounds like extremely loud turbo whistle but if I pull something that puts it in a load the noise cuts in and out rapidly. Sound like Morse Code in a way. Please help me figure this out, makes the truck annoying to drive and especially pull anything. Thanks in advance