Hi,
Your bottom end noise could well be wear on the fibre idler in the Generator drive train. A bad case can sound like a berserk coffee grinder at normal tickover, disappearing at around 2000 rpm. You'll need to pull off the clutch case to see how much backlash there is in the drive train. The noise stems from the generator having six magnetic poles, so the shaft is "notchy" in its rotation as the poles alternately attract and repel each other. At low speeds, this sets up chatter in the drive gears which disapprears at higher speeds as the generator builds up enough inertia to overcome the chattering.
It's almost a characteristic noise on the 175/200 (like clutch chatter on the 350), and is not a sign of any imminent danger until itr gets really bad, but the fibre gear will strip eventually without warning, meaning no sparks and a long walk home (been there, done that!). If you have a selection of gears, fit the one with the least amount of backlash - or try Richard to see if he has any new ones left.
Graham