Whine when driving

[smittyfromPA]

Rear end whine

It seems to be some common problem, when I had mine I learned to live with it and never could figure out if it was coming from the front are since I had 2WD. Or if it was the rear differential. I had heard from a couple Jeep Gurus that this was a common ''Jeep Thing'' for some reason.

Added a Track lock and 4.10 gears in the rear axle 38K miles ago and its whined ever since. I can usually find the sweet spot on the highway around 74-76mph where it quiets down. Diff fluid with friction additive has been changed twice since installed.