Recently purchased a really nice 99 Mountaineer, V8, AWD, 53,000 miles. After driving now about a month, I've noticed a slight whine, I think from front drivetrain, under either normal acceleration, or going up a hill on the highway. Hear it at all speeds. Let off on accelerator and whine goes away. Is this normal with AWD, or is it early indication of a problem. Love the Mountaineer so far. It will replace my 92 Sport 4WD. but gas mileage is less on MM, about 15 mpg, driving with a light foot.
Thanks for any insight!

Sounds like you basic AWD whine! :D Pretty much every AWD makes that noise. Just pretend it's a supercharger... thats what I do.