I've got a knock that comes and goes that my mechanic says is in the bottom end of the motor. After looking at YouTube videos, I think it's my flexplate. After inspecting the flexplate I've discovered that there a currently only 3 bolts holding it to the torque converter. I know there's suppose to be 4. Could this be my problem? I'm trying to locate a place to buy the bolt. Online they are going for $13 per bolt .