Mistery sound when light turns on

Hello

I bought a house a few months ago that was a horder house. There was no flooring or kitchen and was in rough overall shape. Everything is renovated now paint, flooring, doors, baseboards etc. I was noticing bugs like ants and silver fish so I got an exterminator and have a one year contract with him due to this. I also discovered I had carpet beetles which are gone along with the other bugs as far as I'm aware due to the exterminators treatment.

Here's the issue, when it's dark out and I turn on my bedroom lights or the lights on in the room directly below my bedroom I hear a sound for 3 to 5 seconds and then it's gone. It sounds like you are holding the edge of some printer paper and are flicking it. There are no signs of anything like droppings, sawdust, waste, or points of entry. There and no ongoing sound after that.

I have asked my exterminator but he didn't know what it could be. I'm lost on what it could be since there is no signs of anything in the rooms and they are fairly well sealed up so it's not light the light is shining into the walls of there's bugs in them. Any thoughts are appreciated.