The noise is in neutral with the clutch lever not pulled in, idling. Next time try pulling the clutch lever in and even with out shifting into gear the noise will go away. It is louder on some machines than others. My R90/6 it has seemed louder lately. Even if it's not too loud it's always there. Sometimes balancing the carbs makes it less. Somebody mentioned once what it actually is. It's in the trans or the clutch throw out mechanism, I forget. I ignore it, or try to. It is usually possible to wedge one of the probes into a cylinder fin and tension it against the carb cable or something. Same technique is used for the trouble light when setting static timing.