I have an american standard forced air heater and a/c ---the forced air heater is in a closet in the hall and recently when we run it( heat or a/c it buzzes when it shuts down, the only way to stop it is to unplug it. It seems to be coming from the electronic box in the front of unit---thank you RD

Most likley are going to need a new transformer

I think Josh nailed it. The only thing that would cause a buzzing sound would be the transformer. Cheap and easy to replace. Please let us know how things turn out.