I agree with others above that he is being protective and barking at things you may not even be able to hear, or things that you filter out as everyday noises.
We run an air filter and our furnace/air conditioning fan continuously in our house to cover up noises from outside and things inside the house. It helps with our 2 Yorkies so that they don't bark at every little thing.
Having enough exercise or entertainment during the day also helps prevent them barking at school buses and the UPS truck. Even little training sessions performing tricks for treats helps.
__________________ Kristin, Max and Teddy  |