So i was driving my car up this big hill today and it all of a sudden got way louder and started vibrating a little bit, sounded kind of like the car was jumping to a lower gear to maintain speed. I'm assuming it's my exhaust maybe but I know nothing about cars. it was also coming from directly below me or maybe just behind me a little. any guesses on what it is and how much its going to cost and where to take it etc? thanks