A NOISE IN THE D.C. GENERATOR WAS REPORTED AT 12:50 PM & ELECTRICIANS CHECKED IT & FOUND A BAD BEARING ON THE ARMATURE. MSHA WAS CALLED AT 1:20 PM & IT WAS REPORTED DOWN. THE ELECTRICIANS & MAINTENANCE CHANGED THE ARMATURE OUT & RETURNED THE HOIST TO SERVICE AT 8:45 PM. MSHA WAS CALLED & HOIST WAS REPORTED BACK IN SERVICE AT 9:15 PM, SAME DAY.