My wifes Edge developed this rather audible "hum" noise while cruising on the highway. As we go faster the noise speeds up......the sound is like a quiet airplane you hear off in the distance or like a sound you would hear if you put a baseball card in the spokes of a bike. I put the car in neutral while cruising at 55 and this had no effect on the noise....also revved it up while in neutral and still, the noise remained constant.....It does seem louder when sitting on passenger side. At first I thought it was the tires, but the noise remains constant wether on asphalt, concrete or even dirt. Of course the noise slows as the car slows and it just abruptly showed up over the weekend.
2008 Limited AWD.