SO i just bought a 97 gtp sc, it's got some issues that i figured a car it's age would have, passenger window wont go up... when i listen to the engine with my window down i hear a rumbling, like i can hear the pistons. Seems louder than i think it should sound, but i have no idea how it should sound. Guy at Jiffy lube told me it could be the exhaust manifold. I need some idea of what it could be.