Dictionary gives me "drone" and "murmur" but I'm not sure if that's the word I am thinking of. I want to use it to describe a group of people on strike who hear that their demands are not met and the CEO has resigned. They're not shouting, but they're not whispering either. They're restless and confused. I want to say that a certain something (murmur?) was heard among the crowds, to indicate their state.
I think you were spot on with murmur as suggested in the question:
A low continuous background noise:
‘the distant murmur of traffic’
A more relevant example could be:
The murmuring crowd was distracting the speaker.
Or, as a noun:
A murmur of agreement spread through the crowd at the suggestion.
The word you're looking for is mutter. The Oxford Living Dictionary has, as a noun:
A barely audible utterance, especially one expressing dissatisfaction or irritation.
And as an example for the verb:
Back-benchers were muttering about the next reshuffle.
I asked an online thesaurus for synonyms of clamor. Perhaps one of these would suit for the murmuring crowd:
There was a [buzz/brouhaha/hubbub] as the CEO's resignation was announced.
What about "hubbub"?
There was a certain hubbub among the crowd.
Hubbub, from M-W.com:
Noun - a loud mixture of sound or voices : a situation in which there is much noise, confusion, excitement, and activity
Susurration — Vocabulary.com
(noun) 1. the indistinct sound of people whispering
speaking softly without vibration of the vocal cords
Example from Laumer, Keith
The pipes and reeds were shrilling furiously, and the susurration of Yillian conversation from the other tables rose ever higher in competition.
Grumble-According to Merriam-Webster
:to mutter in discontent
: to complain quietly about something : to talk in an unhappy way
: to make a low, heavy sound
- the crowd grumbled their annoyance
- could hear the grumbling among the crowd
- a soft grumble spread through the crowd
For me a din has always had a negative connotation:
[in singular] A loud, unpleasant, and prolonged noise: ‘the fans made an awful din’
The word stir could be used here. For e.g.
The crowd began to stir.
Meaning in this context:
stir: a commotion.
e.g. "the event caused quite a stir"
You may use the word hum.
1 [in singular]
A low, steady continuous sound:
‘a low hum of conversation’
There were wounded who groaned in their sleep or called out, and there was the soft, steady hum of conversation among the wounded who could not sleep.’
a relatively quiet degree of noisiness
Neat that it is an oxymoron describing the muted (typically loud) noise of a crowd
Din may be the a good fit for what you describe, it's more than a low-grade murmur, but lacks the edginess of a clamor.
You could use "chatter" , see examples of usage in the Oxford Living Dictionary https://en.oxforddictionaries.com/definition/chatter
Chatter does not imply a restless or confused state but it does convey animated conversation below the threshold indicating uproar.
A discordant murmuration was heard among the crowds.
a: being at variance, disagreeing, as 'discordant opinions'; b: quarrelsome, as 'a discordant family'
the act of murmuring: the utterance of low continuous sounds or complaining noises, as 'the murmuration of the crowds' — A. E. Richardson; 'ceaseless, inarticulate murmuration of prayer' — Frederic Prokosch
I like the use of murmur, one common idiom phrase I didn't see above was, hush:
"a hush fell over the audience."
Meaning: a sudden silence enveloped something or a group. As the conductor raised his arms, The coach shouted and a hush fell over the locker room. -- thefreedictionary.com