ぶつぶつ
ぶつぶつ · butsubutsu · JLPT N2 · noun
rumble
🫧 Sounds like a string of muttered buts, low protests under one's breath
ぶつぶつ also means bubbling or popping, like a simmering pot. Both senses share the repeated butsu sound: a grumbler's low, repeated protests, or small bubbles going pop.