What noise should i hear from rear end when spinning the tires by hand?

What is your question?

I had the truck, nissan frontier, jacked up recently and when i spun the rear tire by hand i could hear a clunk clunk noise, the gears touching. I cranked the truck, put it in gear and the noise is awful on jack stands. Is my rear end going out or have i just never noticed it? no noise at all when driving in any conditions, 273000 miles on the truck. I did recently change the diff fluid and have changed it several times. But i have never noticed this. Same noise with tires and rotors off too.