Why is there a Grinding noise from rear end of 95 GM van?

some posibilities are Brake lining worn out(metal on metal), no oil in the differential, Gears could be sheared off...ect. very hard to dianose such a vague question. what kind of 95 gm van? venture, full size, cube? when does it make the grinding noise? if it does it when the brakes are applied then it's the first answer. Good luck!