It is saying that america is singing and what it means by that is all the men and woman of america is working during the day. so when it says either the mechanic or carpenter just one of the workers in this poem, is saying that all the noises or sounds are made in the day that the workers make.
Also in this is is saying in the lower half or the second half of the poem it is saying that it is all the noises and sounds at night of the families in america and it is saying that it is all the different sounds are for each individual person they have. so it saying that each person is there self.
In this poem what it is trying to say with all the workers of America are, making there own sound with each noise. Each person is different in America, but it all works together and makes a beautiful song to be as one in America. An also in this poem says that each individual is making there own sound and that each person has there own sound. Which means that each person is there self and no one is the same.