Hey!
Interesting..... You might want to try to observe this during the full moon also... the sound could be even clearer!

Kidding aside. If you are talking about sound in general and not the AC power thing. Yes, I do believe that you hear better at night due to less distraction. And maybe due to darker/darkness surrounding the sense of hearing become more active/sensitive. It is just our primal instinct I would say.

Than again maybe full moon will have some effect too

Take care,
Buddy