Rear direrintial

The rear diff. turns the rear wheels. It is located in the middle of the rear axle. It won't last long if you ignore it. May just need dearing's but if it is driven the cog wheels will grind to dust or drop off this can cause the rear axle to seize up and can be a danger because the back wheels will lock up. If you are going to fix it yourself let me know and I will be able to guide you through the process

Check if any oil in diferential if not put gear oil in it.Don't know how to do your self have machanic check for you. After put oil in it and still grinding your diferential gear damage.

The rear differential is a gear box which converts power from the transmission to the rear wheels. The differential is the middle part of the rear axle. It has a heavy looking tube, the drive shaft attached to the center of it, and the drive shaft connects to the transmission.
The rear differential has a filler plug on one of its sides. A heavy weight oil is used in the differential to lubricate the gears.
Have the oil level checked at an auto shop. Besides having the rear differential checked, I suggest you have all the fluid levels checked, especially if this is a 4 wheel drive vehicle.

The differential is in the center of the rear axle housing. Also known as the "3rd member" the gears inside transfer the drive shaft power to the rear axles.
To check the rear axle, you can pull the drain/fill plug on the rear axle. You can check the condition of the oil inside and check for metal in the oil...a good indicator if you're having 3rd member failure.
Also, check your rear wheel brake linings, and rear axle bearings...they're at the out ends of the drive shaft.
Also check the drive shaft U-joints..the joints that allow the axle to turn angles out of the transmission and at the rear axle. The ujoints shouldn't be loose or rattling.
You may want to have someone scope it out by putting it on a rack or jack stands while the motor is running and the drive shafts are turning. You really want to isolate what the problem before you attempt swapping parts etc. hope all this helps you clarify what's making the noise... and be careful if you're running the car on jackstands...
K

ring and pinion bad... trust me...