Our house was pretty bad when we moved in. Our first night while we were eating a quick dinner a mouse popped its head out from one of the burners on the stove! You know that he must have been very familiar with the kitchen. We moved in in the summer and didn't think much about why they always had all the windows wide open, but the smell finally reached our brains.
When we pulled the dishwasher away from the wall we discovered a LOT of mouse poop. Likewise under the kitchen sink and behind the fridge. The moral of the story; don't just clean what you can see...clean everywhere!
Oh, and the smell continued for weeks, until the dead mice in the walls finished decomposing.