Odd noise

Well driving down the road with windows down and radio off to listen for noises. (very bad habit but never hear one till today) I hear this odd whining noise. I only hear it at 35mph to about 40 and that is all. It's on the driverside. Well i stopped let it sit awhile and hang out with my friend, drive home and no noise. Make turns and no noises after hearing it. What could it be, i even hit the breaks to see if that was it and no the noise keep going. Any thoughts guys, think i should grease the fittings?