I just had my oak floors refinished. House is 15 years old. I am now hearing a cracking/popping sound from the floor at night without anybody walking on it. Any idea what is causing this ?

It sounds like expansion & contraction of the timber, does the temperature vary in the room day/night? You don't say what type of flooring it is, just 'oak' were the joints glued? How loud are the noises?. hey... who is supposed to ask the questions here? Lol... kind regards ade.