The Sound of a Bouncing Ball

Each person managed to stay in the loft for a year before deciding they wanted to leave. One of the reasons was because of the sound of this strange bouncing ball that they could hear in the roof and it only happened at night. They spent quite a lot of time trying to work out what it was no one ever managed to come up with a conclusive answer. We even crawled into the roof of the house in order to try and find out what was making that noise we didn't find anything okay.