Birds in the house

In the front of my house there is a vent for the dryer. Each year that I have lived here a sparrow has made just inside this vent home for their young. This doesn't bother me as it is not my house but it does bother the cats. When standing in my bedroom the baby birds can be heard through the intake vent. When standing in the dinning room the baby birds can be heard loud and clear. While this doesn't bother me it does drive my cats crazy. Buster wants those birds so bad. He will go up stairs and look down the vent then he will run down stairs and stare at the ceiling. He will run back and forth for hours. Aphie is not smart enough to figure where the noise is coming from so she just wanders the house listening. I just know one of these days Buster will figure out how to take the top of the intake vent and get those baby birds. Crazy cats.!