Diff noise diagnosis

Alright so when me and my cousin bought the dart back in august 2010 the previous owner told us that the rear end was very loud.
Now after we towed the car back to my cousin's place, we started tear down
Later on i remembered how she mentioned the rear diff was making a noise so i went under the car, and took the diff cover off. Grabbed a light and took a good look. Well the only thing i could see wrong was the lack of oil. There was like 2 drops. I was expecting oil to pour out when i removed the cover, but nope.
The ring and pinion gear were in great shape, no apparent damage.

So why do you guys think it was so loud? Improper gear mesh, something else, or just because the lack of oil?

Duh? Yea the lack of oil. Fill it up and try it out, the damage may already have been done.