Tonight, after 8 months, I will finally be able to sleep uninterrupted. The source of the weird (and loud) irregular sound that woke me up several times per night, like stones hitting each other, has finally been identified. It was a bunch of CDs hanging from the rooftop to scare away birds from nesting and it used to be fixed to the ground. That wire has been cut 8 months ago, causing the CDs to hit a structural element when the wind moved it. I fixed that. I can finally sleep tight again :)