murmur is one I'd use for a low voice talking crowd. I'm looking for more alternatives.
I would go for babble, which can mean
a continuous low or confused sound, especially the sound of several people talking
disorderly agitation or milling about of a crowd usually with uproar and confusion of voices
Susurration is a nice choice, if there is a whispering quality to people's vocalizations. Groups of people around you can make many different sounds. It depends upon the specifics of what's happening and how people are feeling and acting. You've gotten lots of good suggestions for various types of sound.
The crowd susurrations were liquid in his screwed-up ears. Cory Doctorow, The Makers
n susurration speaking softly without vibration of the vocal cords
n susurration the indistinct sound of people whispering "a soft susurrus of conversation"
L. susurratio, fr. susurrare, to whisper: cf. F. susurration,
hypernyms :sound, speaking, speech production
Rumor can also be used in this context:
a soft low indistinct sound; murmur
My own preferred word is susurration
According to Dictionary.com it means:
a soft murmur; whisper.
Three of my favorite words in the English language describe this:
hubbub - a busy, noisy situation caused by a crowd of people.
hullabaloo - a commotion; a fuss.
brouhaha - a noisy and overexcited reaction or response to something.
Out of them all hubbub is specifically a word that describes what you mean.
Well, personally, I like din since it's always appropriate if the noise of a crowd is unpleasantly loud enough to be noticed in the first place.
As far as things people haven't already mentioned, there's also
The radio, film, TV, and game industry jargon for indistinct crowd noise.
A low, heavy sound, continuous but varying; a murmur, grumble, or growl, esp. of discontent; noises of restlessness, or an early indication of tumult and uproar...
A meaningless, rambling or derogatory spiel; babble; a disorderly assembly of people, esp. of the lower classes...
A rapid succession of short vocal sounds, as some bird calls; rapid, incessant, trivial speech; prattle...
US chatter; Scots grumbling, nagging speech.
A rapid succession of short, sharp, percussive sounds; a state of uproar; lively and empty chatter, babble...
A perhaps less obvious, yet colourful choice would be 'dissonance'.
a mingling of sounds that strike the ear harshly
a mingling of discordant sounds; especially, music