To grumble; to complain in a low, muttering voice, or express discontent at or against someone or something.
To speak or make low, indistinguishable noise; to mumble, mutter.
I couldn't hear the words; he just murmured a lot.
To say (something) indistinctly, to mutter.
A sound that murmurs.
the murmurings of trees in the wind
A complaint against something.