Very odd noise, need some help figuring out if I need to attempt to have the dealership recreate.....could be a long process.
2010 22K miles; EL 4x4
When driving on interstate (anywhere between 60 and 75) at times a hum will start (probably every third trip). It sounds like it comes from the passenger side. Its reasonably loud. When I accelerate hard it goes away, when I coast or have really light acceleration it comes back. Its a solid hum/whistle...it doesn't change pitch.
jack up the front of the truck with the motor running
spin both of the front tires. if the front driveshaft rotates, or tries to...it means you have a hub that is failed, or the some part of the vacuum system has failed.
after you hear that noise, pull over really quickly and do a touch test of both rear rims. if the e-brake is dragging on either rear wheel, the rim will be rather hot. You may hear 1 side dis-engage, but it's better to be for certain. the 07+ Expy is based on the 04-08 F-150. The 04+ F-150 has a bad habit of having the rear e-brake freezing up.
What i had happen with mine was that the rotor cover was rubbing against the rotors, this is caused if you recently swapped tires and the cover was slightly bent. All you have to do is hit it hard enough back