Ram Differential Question

I have a 1997 Dodge Ram 1500 ext cab with 5.9L 360 V8 and automatic transmission. The differential is the standard Chrysler 9.25" gears without posi. My question is why is my diff whining? Whenever I give the truck gas the diff whines. It sounds kinda like new tires "sining" on the road. Is this a common thing or is something wrong with the truck? Thanks

Low fluid level? Wrong fluid?

Had the same prob with my 98 had to replace the whole rear end. pull off the access panel and check the gears replace the fluids

I checked the gears and changed the fluid. Everything checked out. It whined when I got it and I asked about the fluid before purchasing it so it has the right fluid in it. I guess I may have to change it. I want limited slip anyway.