My 08 still makes that sound that I cannot figure out. Dealer is still stumped. It is mostly on happens on acceleration. Does not do it when cold, kinda sounds like a bad speedo cable, ( I know we dont have one). Both Exhaust manifolds have been replaced, you can only hear it from inside the truck. Tried the grounding kit and most everything else I have read here. It is definately tied to the gas pedal, more pedal, more noise. Dealer says they have heard other titans do it too. Almost like a slight whistling thru the dash vents, but the fan and a/c make no difference. Anyone run across a fix for this?