The bearings are located with eyeless wire c clips so are awkward to remove without them making a break for freedom at high speed, then the bearings have to be drawn off the axle shaft with a suitable puller. The bearings are on sealed on the outer faces so you can grease them on the insides without removing them from the axle. You'll probably find that the grease is still there but has just worked out of the races - the sound is probably from grit and dirt in the spring seals at the ends of the cartridge, easy enough to clean up if you strip it down.
