We have a colourbond roof and it can make certain noises (of expanding/contracting) when the temperature quickly changes outside. Could it be that?
A couple of weeks ago I went into my DD's room when it was around mid morning. She was upset as there was this strange tapping noise going on outside her window. It had woken her up a few hours earlier and wouldn't stop. (She has Aspergers so has sensory issues with noise). I put my head close to her window and thought it was some workers building a house in the distance. When I moved from the window, it sounded like it was just outside the window. I pulled her curtain open and saw what was making the noise.
She'd placed a solar powered flower on her window sill and the noise was the leaves moving - when the sun reached her window it started to move.