Radar isn't a perfect system for showing where rain is falling. Very often, the radar shows "stuff" in the air, or obsticles above the ground that aren't rain.
For example, birds and bugs can show up on radar, especially in the evening. This is because in the evening, as the atmosphere near the ground cools, the denisity of the air near the ground begins to increase. Having different density air at different heights causes the atmosphere to act like a lense. Since radar beams are just like light, they bend, and toward the ground in the evening, exposing the beam to much more of the dust, birds, and bugs near the ground. This results in false echoes. Think of a mirage, it's the same effect.
On the radar maps, we have a feature to remove "ground clutter". But, it also tends to remove some of the real precipitation. The best solution is learn to identify the false echoes through experience.