I had my exhaust manifold replaced at the dealer last Wednesday.When I picked up my car and started it,there was a loud,scraping noise.I told them about it and they had a mechanic take a test drive with me.I turned it off and restarted it.It didn't do it.Today,I started it and the same thing happened except this time,my gas cap light came on and stayed on.What could this be?I'm worried that they've fixed one thing and messed up another.