Bats!
This is a bit of a saga, so I’ll do a quick intro before I get to the guts of it. I purchased a house in December 2006, and after a month or so living there I noticed a scratching noise in the walls. I pulled out the air-con, and looked into the wall cavity, and there was a roosting bat. So I did a bit of research into them, and decided they were getting in around the air-con, so I left the air-con out one night, and late in the evening sealed up the hole, and put it back in....