Hey people

Got a question.

Earlier today I let some guy test drive my car and now I hear this rattle when Im driving normally. You can hear it the most in third gear. Not flooring it or anything but just kinda stepping on the gas you hear the rattle, I don't know how to explain the rattle noise but Its annoying. Performance wise I dunno if its affecting it at all, but when I do get on it its like im not getting detonation or something and gas smell like crazy.....I think my mas is affecting that part but i dunno.

Any suggestions???