My son has a 2001 Honda 400ex, it has some mods. It's been making a really loud bad sounding noise when he is trying to start it. It's not what I would call a grinding noise but a metal hitting metal noise kinda like a flywheel gear not engaging into another gear wheel but a lot louder. My husband has taken apart the left side case and found that the flywheel was damaged as well as the one way gear that the starter engages. We have replaced flywheel, starter gear, and bearings between those two. Everything turning over by hand is smooth, no noises. But when they try to start it that's when they are getting the metal hitting metal noise. I can try to add a video of what it's doing and sounding like in just a few. Any ideas of what is wrong and fixes would be greatly appreciated.