Wining noise in 4wd

I'm getting a wining noise when in 4wd and accelerating or decelerating. If I am in 2wd or just coasting in 4wd, no noise.

A little background. Just purchased the jeep from my father in Saint George Utah. It's a 99 Cherokee Sport with only 55,000 miles on it. He drove it very little the last few years. It's an automatic with 456 gears and ARB lockers.

I'm wondering if it sat too long and something dried out.

Pull the covers and inspect at least.

you didnt give much specifics about when it happens.
4Lo will give you some whining, but barely more than noticable.
check the oil level in the Tcase. often neglected and almost always low on any used vehicle.