My car is a manual. Sometimes when I find myself having to slam on the brakes kind of hard, I hear a load "knock" noise that sounds like someone is denting in a piece of metal. Then, when I proceed from the stop, the "knock" noise happens one-two more times...sort of sounds like it "knocks" out of place, then has to "knock" back into place. It also can be heard sometimes if I don't time my clutch and gas pedal right when coming from a stop. Sounds like it is coming from towards the front of the car. Not sure what the cause is and had no success looking online. Is it anything serious?