It's because the house knows that the music it makes is for the night. During the day the music of a house is about people living their lives, the sun, birds chirping, laughter or angry fighting, our voices make the day music. Our actions make it.
But at night, we quiet down enough that the house can write us a symphony finally, and we're on the right wavelength to hear it.
Sometimes nature plays along. Crickets, the wind creaking at the windows, tree branches nearby hitting on things, all of those kinds of things. I love it when that happens.