If stored in a garage make sure there is mouse bait in the garage too kill those pests. If stored outside under cover make sure there is mouse bait somewhere in the interior and under the hood. You won't believe how fast mice will make a home out of a parked car. I found a big old mouse nest made of pink fiberglass insulation down in my XF engine compartment when I had to pull the battery for replacement. Obviously it was parked somewhere close to accessible insulation for an extended period of time at some point. I also found a mouse nest inside a box inside my construction trailer that was parked about 10 yards from my house made of pink fiberglass insulation. Glad they took up residency there with my home's insulation instead of inside my walls.