Earlier while driving, my 1992 Cadillac Deville started accelerating on it's own.

I know nothing about cars.
A friend came by, he pulled the cover off of something, and used some pliers to fix the problem. It did fix the problem, and he left. But I test ran it, and it knocks several times, when I shut the car off, then stops. Sounds like a knock on the door. Any ideas?