60 mph

At 60mph and above there is an odd sound coming from the front of my wife's 2004 expo. Now i kinda think its the half shaft bearing but i can't be certain. i took the tire off and nothing was obvious any suggestion?

Is it a 4 wheel drive? Is it working? Here are a couple of links from the F150 area of the forum since they have most of the same components.
http://www.automotiveforums.com/vbulletin/showthread.php?t=1138152
http://www.automotiveforums.com/vbulletin/showthread.php?t=1122266&highlight=vacuum+hub
http://www.automotiveforums.com/vbulletin/showthread.php?t=1122268&highlight=vacuum+hub

Turned out to be the front diff

The electric component went out and so what ever the vacuum was supposed to be doing it was not. After that was replace the fwd gear box for 4wheel drive was replaced. oh yeah and i ate that in the pocket.

I didn't have the tools or the means to do it myself. but i really hope this helps someone else. trouble shooting alone was brutal.