I have 2004 4.7 4 x 4 quad-cab with 78,500 miles. I hear whistling going down the express-way.I let off the gas pedal and it stops then I apply the gas pedal again. Everything sounds normal and I don't notice any transmission problems.
If the whistle is dependent on throttle opening, I would look for a disconnected or damaged vacuum line or some kind of vacuum leak? There may be a vacuum routing label under the hood to give you locations.