ok so my truck started making this clanking sound and i cant figure out what it is, im pretty sure its coming from the engine, i put a different pipe on to see if it was that and it still made the sound.it sounds like there is a little piece of metal inside of the engine bouncing around so i took the backplate off and i didnt see anything inside and then i took off the plug and still didnt see anything. does any body know what it might be???????????????