Ok, so I have an 06 Yz450f 50th edition. Its clean and running good. Just makes a knocking/pinging sound. I've been told this is normal. It runs perfect and I have heard other bikes of the same year or a year newer and they makes the same sound. Now I just want to know what would cause all the noise? Are theses engines just loose but reliable? I am paranoid about it and I am used to a motor that sounds tight. I'm not trying to fix it, I just would like to know what causes it all. Thanks alot. Also today while I was riding today I was listening very carefully to the bike. If I hammer on it wide open like 3rd through 5th then come to a stop the noise is 15 times quieter for about 30 seconds. It makes no sense to me.