I fought some bats and left some guano in a ruins room. I could hear the flies buzzing around the guano in other rooms in the ruins. But what's weirder is that I could also hear the same flies while in my house. I've noticed the flies sound continuing at times when no manure or guano is nearby, but this is a specific instance that I'm able to report.
Leave manure/guano in a ruins room. You can hear it while in the house in the hamlet.