So opened a case with Ford. They insisted that I take it back to a dealer for diags which I can understand to a point but of coarse the dealer I take it back to looks at it and says all good - no noise, normal performance and no oil leak. So here we are a few weeks later and today in a very cold drive I actually got the surge noise while on light and steady throttle. Noise did go away but I am thinking its a sign of the "new" turbo progressing to fail. Truck now scheduled for diags at a tuner shop who knows turbos. What a bunch of crap from the stealership.
And yes to the post above that is the exact noise. Sometimes I hear it 2 or 3 times in a row and the tone changes. I am 99.9999999% its the sound of the turbo spooling down. Why is a total mystery other than a vague guess that it or the wastegate valve are failing. Very unfortunate that the wastegates are not a replaceable part on these years.