on my lincolnls v8 in rear of car when i drive it sounds very loud on 2000 Lincoln LS

it sounds like a whinding sound i was told differential,and also told drive train

Asked by for the 2000 Lincoln LS
The differential is part of the drive train. Has anyone checked the oil level or have they said it is differential bearing that have failed. Have the checked the rear wheel bearings to see they are not the source of the noise?