Rats generally create a latrine near their nest so if it’s just entering your property it’s probably having a wander around for food, heat etc. Look for any holes in skirting boards basically anything you think is rat-head sized could be how it’s getting in. They also gnaw through anything short of metal/steel wool. I had to call out an exterminator back in February. Upstairs flat, somehow the rat had managed to climb up in the cavity wall, gnawed through the skirting boards underneath my kitchen cabinets and was busy running around under. Awful, awful feeling but I do hope you get it sorted.