muttering   
fimonomononana
grumbling, muttering [Hallanger 1973]
monomonona
muttering, grumbling [Hallanger 1973]
ngonona
a low muttering, a low grumbling, a low murmuring. [Richardson 1885]
ngonongonona
a low muttering, a low grumbling, a low murmuring. [Richardson 1885]