So I let my 20 yr old take the WR426, 2002 out for a 70 mile ride. I'm sure he I over revd it. So I warmed it up sounded fine, took off and when I decelled to a stop sign I heard a slappidy clank, very suddle, but can be heard best if your hands are on the bars cause you can slightly feel it. It's slight enough that it took a few stop signs to determine there is somthing funny sounding. No performance problem, and no sound when riding. I Have narrowed it down,,, you can have it idling on stand, just give suddle throttle and as the throttle comes back to idle you can hear the slap. What you think ? My thoughts were, if it was piston slap I would hear it during other modes of riding. Maybe that cam chain tensioner broke some teeth and pulled back,, loose cam chain spanking due to looseness ? Again, starts and runs great, not slap at all while riding,,,, but if coming into turn hard with clutch pulled in and rpm comes close to idle before nailing it you will hear it. Does sound like coming from top of jug.