As Mac was mentioning, a lot
of that "sketchy bearing sound" is coming from the clutch. The gear case cover itself acts as a resonator and amplifies what's already an annoying sound. I quieted mine down quite a bit by coating the inside of just the cover with a few coats of rubberized undercoating
As for why the lil ones seem to make more noise... I think that might just be a random luck of the draw more than anythin' else.