so I had taken to a race everything went fine minus some fuel boil causing a no start, any way then I took it on a road trip and then I noticed when I start it up especially when its cold I get a real loud knocking at first I thought it was maybe a valve not seating and explosions in the exhaust (still not ruled out) Then someone suggested it might be a flexplate/torque converter issue which I think it is because this morning I started it up and put it in reverse nothing while the knocking was real bad put back into park and then into reverse again the knock calmed quiet a bit and it moved so pulled it up on ramps and looked at the flex plate and it looks nearly new which it should because it is. so I took a video notice it goes away when I rev the motor

Just a thought, did you check the torque converter bolts, were they tight? I've had some just loose enough to start hitting things.

okay I feel stupid as I probably should no I didn't check them when I took the video because I didn't have a 15 mm with me but I since have and two of them were loose couldn't find the torque spec so I just tightened them enough until the engine spun and now no more knocking, I will probably pull them all out and lock tight them so it doesn't happen again