While driving to the airport the other day (F-350 6.0)I suddenly noticed what sounded like a flute playing the C note around the center of my dash. It was during a hard acceleration at freeway speeds and the pitch increased a bit with the rpm's. It comes on at 2500 rpm's. It sounds like vacuum leaking but is not a hissing noise. I am thinking it might have to do with the climate control which is not electronic, however,it does not matter what position the controls are in. I can not duplicate the sound at a stand still, only under load. I looked behind the glove box at some vacuum lines and the servo but it all looks tight. I don't think the sound is under the hood, it is pretty much center cabin.
Anyone experience this?

 

You might try asking in the 6.0 forum also, in case this is an issue with the engine instead of the turck.

 

I had a similar noise, except it came from the brake pedal area. I would check around your coolant reservior for a white residue. And look for the same residue around the underside of the hood right above the reservior. If you see this residue you need head gaskets.