Over the progresion of time my WR is getting quite a sort of air & metal noise about the engine. It happens only once the bike is hot, never in idle, from about 1/4 to peak RPM. It is a engine noise as it happens whether the clutch is in or out, any gear, and it goes in tune with the engines RPM whether the bike is moving(in neutral) or stopped. I have changed the oil, checked the level, for it to still occur. I have confirmed oil is reaching the top of the engine via undoing the bolt that connects an oil pipe(carby/kick starter side) to the top of the engine. Radiator's are full and both get hot with operation. What could it be? Worn timing chain guides?? For that old car engine noise it makes, it still goes hard as if I've just bought it. Traveled 7000Kms(no tar work). 00 WR400.