CM871 Tune

[Chamberpains]

Is the "rattle" at 1300 rpm+ in gear and out? Through every gear? Or only in the top gear 1300+, meaning 60 mph+? Maybe speed related? What the closest sound you can compare the rattle too? Do you feel any shaking?
From your description of the area it sound like your clutch brake or throw out bearing on the clutch may need some attention. Possibly even the forks or linkages. But if I where you, I'd thoroughly check the trans and rear ends (fluid for contamination and signs or failure) and the u-joint while your at it.