  Extending a Boltzmann-Langevin theory to magnons, we show a universality of
current-noise suppression in diffusive systems against the difference of
quantum-statistical properties of bosons and fermions. To this end, starting
from a quantum kinetic equation for magnons subjected to thermal gradient in
dilute impurities, we derive a bosonic counterpart of the semiclassical
Boltzmann-Langevin equation for electrons and evaluate a magnonic current-noise
in the diffusive insulating magnet. We theoretically discover that compared
with a Poissonian shot noise of magnons in an insulating ferromagnetic
junction, the magnonic shot noise is suppressed in the diffusive insulating
bulk magnet and noise-to-current ratio (Fano factor) at low temperatures
exhibits a universal behavior, i.e., the same suppression $1/3$ as the one for
electron transport in diffusive conductors, despite the difference of
quantum-statistical properties. Finally, we show that our predictions are
within experimental reach with current device and measurement technologies.
