Urine Odor. Rat urine has a musky odor. You can easily smell it with large infestations.

Rub Marks. Oily rub marks are left in places where rat travel along walls. If rub marks smear, you know they are fresh. .

Runways. Rat pathways are generally along the attic walls & in insulation.

Noises. Rats are nocturnal. At night they often create scratching sounds as they run inside walls and along floors.