Weird noise while cruising

[07OUTLAW]

Ok, I need a little help here guys..........

Last night I went out to see my folks, when I got on the highway I noticed a weird noise (it started right around 60mph) It almost sounds like a high pitched "white noise", not quite a whistle, not quite a squeal, not really a whirring sound (my GF says it sounds like a whale )

Anyway, it starts right around 55-60 mph and stays constant at any speed above that, if I slow down it stops right around 55. On the way home last night it did it again BTW - on the way out there it was -15* - -20* F, and on the way home -30* - -20* F, if that matters at all.

I'm baffled, my dad heard it too, and he has no idea either, and my GF still thinks it's a whale

[2005F250]

Is it coming from the rear of the cab?

[07OUTLAW]

It's kind of hard to pinpoint, but I think it's coming frrom the front end somewhere.