ok so i went out in the snow today in my 91 cherokee and was out climbing 3 foot hills onto the road, and when i engage my 4LO and climb the hill the drive side rear end makes like a squell sound. like brakes squilling just louder. any input would help. D35 axle

 

Nothing changes in the rear end when you shift to 4lo. If the rear end doesn't make the noise in 4hi or 2wd, it's not the rear end. May be the xfer case.

 

you might have a rock or some small debris in your brakes.
chris