Without studying it closely, do you think it 'is' grinding on the case as by memory they're machined there for clearance where the teeth wizz past but suppose wear in the outer cover [not un-common] could let it move slightly over on the outer end & if it's a close call to start with then it might just make the difference [but don't think so sorry]. What i'm wondering [or thinking] 'is' the ratchet staying partially engaged [not releasing fully back out of the way]. Could operate it [plug out-or clutch off] & see how far it moves back when against the return stop. Maybe pack the shaft more to the outer cover side if possible which will take the gear further away from the ratchet in the returned [up] position--[fully up that is] as only disengage on the last little bit. Might be able to bend the steel stop to make it pull the ratchet more out of the way. Dot on the shaft [without looking] is possibly only to do with kick start spring tension & is still important within reason from the spring point of view. Might be a bit of leeway there to wind the spring up a notch to make sure the lever is hard up after starting. A static test [for the ratchet] would be--plug out & turn the mag flywheel backwards by hand & see if it comes to a stop due to the ratchet picking up [seen that cause havoc on old points ignition AG bikes running backwards, touch the kick start & bang--all over--or all over the floor more like. If yours revolves backwards it might be just touching the top of the ratchet but not enough to catch & lock backwards but enough to to rattle when running. If i'm up the creek then sorry about that--open another beer & carry on. Cheers. ps, with motor running try pulling the shaft towards you, if it's got say a couple of mm end play & the noise stops then pack the other end --something like that.
