Noise can come from dry lubricant, grit, a loose axle nut, a damaged shield or a bearing that has reached the end of its useful life.
Check the easy things first
Make sure the wheel hardware is assembled correctly and the axle nut is not too tight. Then inspect the bearing for dirt, rust or rough movement.
Noise is a clue
Do not judge a bearing by sound alone. Spin it by hand and feel for roughness or sticking before deciding whether to clean or replace it.