I had a similar experience. It was a dark summer night, 03:00 o'clock. Me and my partner were semi-asleep when suddenly a loud noise from the kitchen wakes us up. It sounds eerily electro-mechanical. And then some seconds later, it happens again. And again. And again. We had no pets, no one else living with us, so we were concerned someone had broken into our apartment in the middle of the night. I mustered up the courage to enter the kitchen. There are no people there, not even a small animal. I turn on the lights and confirm that. But I see the lid of our bin is open. It was a stupid purchase from costco, this household bin with an automated lid that used a depth sensor. Turns out, there was a slug walking all over the sensor. This is how we figured out we had a big hole somewhere under the kitchen furnishings that was a source of slugs. We moved away in less than a year, but boy was it not fun to think about the slimy mess that may have been left on the countertops.