I have a 2002 AWD Mountaineer that has a loud whine from between 1500-1800 rpm. While it doesn''t disappear Completely at high revs it does reduce dramatically. Can''t tell if it is front diff/u joints/drive shaft. Any ideas or what I should check?

A little more info on this issue - only happens when under power. As soon as I let of the gas it stops. Don''t feel any vibration through the pedal just the noise during acceleration. However, there is a bit of a vibration if I just barely let off ofthe pedal while keeping speed constant.