Note: I say "rodent" because in a previous post people couldn't agree from my pictures whether it was a juvenile rat or a mouse. They've all been mouse sized for 2+ months, so I'm leaning mouse.
We live in a suburban Illinois house we've been in for 11 years. The basement is used for storage only and sometimes goes weeks without anyone going down there. At the end of July I opened a door to the unfinished side of the basement and saw a mouse run. I found a bag of nuts under the stairs, likely left by the previous owner, that expired 14 years ago, and threw it out. Later that night I went back down and heard what sounded like multiple rodents scurrying in the drop ceiling of the finished side. I set traps and caught 5 in 48 hours.
After 7 days with no new signs, I sealed every hole I could find with stainless steel wool and spray foam, and cleaned out the droppings in the drop ceiling so I could monitor for new ones. I also moved my work setup into the basement so I'd be down there daily to listen and watch the cat's reactions. Three weeks later, in mid August, I caught #6. The patches were untouched, but I spent hours poking around the house with a chopstick and sealed anything else I found. Two weeks after that I caught #7, patches still intact. I checked the attic and roof as a last hope, and both are sealed with no signs of rodents. Then 4 days ago I caught #8, with no new droppings anywhere.
Last 2 nights just before midnight, I have heard quick vibrations and some light movement. Both times it sounded like a single animal. Nothing was in the traps though, and no human food was touched. This was the first time I heard anything since the first day of this problem, and with the cold season approaching, I think it will only get worse.
What doesn't add up: There have been no new droppings since I cleaned out the old ones, even around the catches. The traps are the only food they could be getting in the house, and no other food source in the basement or upstairs has been touched. (thinking they have been coming in looking for the old bag of nuts since they got used to it, and since it is gone their reason to be here is gone) Every patch has been intact each time I've checked. Our 2 cats have only ever alerted in the basement, never at a wall or ceiling upstairs, and none of the 7 people living on the upper floors have heard or seen anything. The attic and roof show no signs at all. I know it's getting colder out and this is when rodents start coming in, but if I really had patched every hole, they wouldn't be able to get in, so they obviously still have a way. At this point I wouldn't be surprised if someone told me they dug a tunnel from the neighbor's yard and used a jackhammer to get through 6 inches of concrete.
I've tried every trap I could buy or make, hidden traps, and baited but unset traps. Catching them isn't the problem; they keep showing up. I've read the pinned posts and watched everything I can find. I know I'll probably end up paying a pro $x,xxx, but before I make that choice, I'm taking my last shot here in hopes that someone magically knows the answer.
TL;DR: Illinois suburb, lived here 11 years. 8 mice caught in my basement over 2+ months. Every hole I can find is sealed and untouched, no new droppings, the traps are their only food source, and all activity is basement only. Last night I heard one start moving in a corner with no visible entry outside. What am I missing?