Mice in a crawl space may reveal themselves through scratching sounds at night, droppings, chewed openings

https://daltonnzom925.talesignal.com/posts/why-old-attic-insulation-ruins-your-indoor-air-quality-2

Mice in a crawl space may reveal themselves through scratching sounds at night, droppings, chewed openings, nesting material, or even unusual pet attention.