The linear bearing moves along the length of the rod (obviously) and should feel smooth and almost friction free. They won't turn very well around the shaft, i.e. as if you were turning them with a spanner. That might be obvious, but I think it's worth mentioning.
They can sound scratchy, but the important thing is they move freely along the length, so if you've got bearings that are stiff, that's not good. It will put additional strain on your stepper motor making it run hotter, won't move as fast, and the whole thing will make a lot of unpleasant noise.
I'd be tempted to get new bearings now, it's a pain replacing the Y axis ones, the Z axis is a bit of a pain, and the X is quite easy. The Z axis is under the least stress as it moves slowly and infrequently, the Y axis ones (under the bed) are under a fair bit of load, but it is well spread across the bearings and generally feels easy to move. The X axis is under considerable load and you get a twisting effect from the carriage which stresses the bearings even more.