I'm new to the forum, so, bear with me. I have owned a 1998 yz400 since new, the bike has been nearly flawless for all these years. I have rebuilt the engine once, only after a failed 3 gear rattled into the top end. Recently, I rebuilt the top end only because I was feeling guilty about not doing anything to it in years. I ride the bike two, maybe three times a month, mostly in the desert of southern calif. Running a 15/44 gearing. After installing the new weisco and having about 4 trips on the top end, I noticed metal in the filter. I flushed out the engine and new oil and a clean filter installed. Ran it again and the same thing, more metal. I tore it down, and to my amazement, except for a little gear spalling it looked great. No bearings spinning, piston looks good, nothing unusual. I replaced the bad gears and now i still see a little metal in the filter again. One thing of note, when I hold the throttle open steady, whether in gear or not, I hear a pulsation from the engine internals. Has anyone have any idea what is going on??