It has to do with the interaction of light and sound. The sun produces virtually infinite photons (packets of light). Even though these are infinitesimally small, they still have some mass. Sound, however, travels in waves through matter. Have you ever heard the term, "In space no one can hear you scream"? That's because there is no matter in the vacuum of space. During the daytime, the huge amount of photons entering the earth's atmosphere from the sun saturates the matter in the atmosphere. This makes it much more difficult for sound waves to get through, and accordingly, they are diminished the further they have to travel. Think of it as the difference between walking on concrete and walking through waist deep water -- the increase in matter inhibits the locomotion of the sound waves.
You might also have noticed that this effect is diminished when you are in a well lit room at night. The artificial lighting acts as a proxy for the sun, injecting the micro-atmosphere in the room with light photons. Because it is essentially the same as being in daylight, you will not notice the noise-increasing effects of being outside in the dark as much.
Why you are hearing sounds louder in your house could be due to several reasons:
(1) Your home is not very well lit
(2) The items you are hearing are proximately close to the outside or are coming from outside
(3) Your windows are diffusing light photons into the dark outside, negating the effect of the lighting and making your house less saturated with light
To test the effect, you should go into an internal room with no windows in a well-lit building. You will notice a marked difference in the loudness.
Hope this helps.