murmur

[1]	mumble , mutter , whisper
[2]	complain , grumble , mutter , moan , lament , wail , (Colloq) grouse
[3]	mutter , grumble , croak , gnarl

[1]	mutter , undercurrent , undertone , muttering , murmuring , background noise/sound , rumble , murmuration , mussitation , rumbling , mumble , mumbling , drone , droning , buzz , buzzing , murmuration , murmuring , hum , humming , whispering , (Formal) susurration/susurrus
[2]	muttering , murmur vowel , complaining , complaint , grumble , grumbling , (Colloq) grousing , grouse
[3]	heart murmur , cardiac murmur
[4]	grumble , grumbling , murmuring , mutter , muttering