Here is the symptoms. I have a whine that is only present when you have your foot on the gas. And it only happens between 35-65MPH and then it either goes away or gets drowned out by road noise. The dealer is assuring me that the noise is coming from the front. Does that diagnosis sound right for the front diff? They did replace the front drive shaft because the CV joint was bound up and they say that caused extra wear on the front, does that claim sound rigth? If I do switch into 4hi I don't notice any change in the sound. However the front diff does growl a little if it's in 4hi and you excelerat or put it under load? I am really confused as I can't find any strait answers and I don't know to believe the dealer or not.
If the front diff does need serviced or replaced how much can I expect the dealer lighten my wallet?
98 Explorer, sohc, control trac 4x4, 5r55e tranny.

Thanks!

 

Just got off the phone with the service dept. They said the noise in the front end is "normal" and it's the ring and pinion gears making the noise. I am mechanically literate so how hard would it be for me to yank the axles, drop the drive shaft and drop the diff and replace the ring and pinsion gears and bearings?? Or is it so complicated and precise that it's not worth me trying it myself?
Thanks!