My kids 04 230f started making noise recently kind of a knocking noise. When started and at idle its good but if I blip the throttle the noise starts when it returns to idle and doesn't go away until its shut off again. I was certain it was the cam chain, Sliders or tensioner so I started tearing it down. The front cam guide has a wear groove in it and when at TDC the marks don't line up so I would think stretched timing chain. Just because I grabbed the flywheel and it has some up and down play. Read a few threads and found others had some up and down play in the flywheel also and said it was somewhat normal on this bike. Hard to believe that would be normal but question is could this be the source of the knock?