Just the thought of rodents under my hood gives me the shivers! Been there, done that. Tried everything from leaving the hood up, lights, setting traps, used a commercial product that stank to high hell, etc., and that pack rat (I saw it) just laughed at my efforts.
One important note is that their urine scent attracts others. It is imperative you get rid of their scent. I took my van to a car wash and power washed under the hood. Removed the battery to get under the battery box, which seems to be a favorite place for the little boogers. In the end, I left where I was, drove 500+ miles in the Summer heat. Don't know which of these attempts worked, perhaps a combination of efforts did it. Especially relocating.
I eventually sold that van and recently bought a Class B. Weeks after, I had someone replace the batteries and when I picked it up, he told me there was a nest under the engine battery box! Nooooo!!! He cleaned up what he could before installing the new battery, I washed under the hood when I got it home, and once a week I go out there with a flashlight and check for signs of rodents. I HATE the little *******s!!! As for a "humane kill", bull!! Quid pro quo -- it made me suffer so I don't care how it dies, just so it's dead!
Just thinking about that battle raises my heart rate and blood pressure. Have I said how much I HATE them??!! Lemme at 'em!