I did some looking around this morning. I looked as best I could behind the washer/dryer and didn't see any holes of any size. However, since I caught this 2nd mouse in the kitchen I looked around there and I saw a really big hole (baseball-sized) in the wall under my oven. I pulled out the storage drawer at the base, and there is a big hole in the wall where some wiring for the oven comes into the apartment. I put down about 6 new traps today with the jarlsberg they seem to love so much. I told the maintenance guys about the hole, so we'll see if they bother plugging it.
The most confusing thing for me is why these mice decided to suddenly show up in my apartment. I'm not messy, I clean regularly, I don't leave food/drink out. I haven't noticed any containers being chewed into (and I literally have maybe 5 - 6 containers of food in my cupboards anyway as a single guy). It's not even winter when they might come in purely for the warmth.