During the night, distant sounds become louder than during the day. This is due to:
Refraction of sound waves.
After sunset, the surface near the earth cools down more than air in succeeding layers above. Hence, the distant sounds can be heard as the sound waves get refracted and reach the receiver which is present at a distant point. During the day, the sound bends away from the ground; during the night, it bends towards the ground. Hence at night, you have additional "sound" reaching you, making it louder.