I literally made thousands of dollars when I was still a Tech just on rodent damage so get that bastard out of there. They love wire insulation, it almost sounds like you might have a pack rat which is even worse. When they would get under the hoods we would tape a box of D-Con under the hood. Whether it's a mouse or a pack rat it will do it in. I've seen them do things you wouldn't believe. I had a Tacoma come in and there was piss dripping from the heater core box and the fan was making weird noise. He had gotten up in the duct work through the floor vents and built a nest in the fan box. I had to replace the fan box and fan motor and the detail shop had to shammpoo the carpets. I hate the little bastards with a passion.