Public assembly and mass protest are increasingly common features of our political landscape. The recent women’s marches, the mass protesting of President Trump’s so called ‘travel ban,’ Black Lives Matter, the Arab Spring and the Occupy movement are centred on the bodies in crowds in the streets. This paper examines the sound of the crowd, arguing that the sonic offers a productive framework for attending to the collective yet heterogeneous nature of public assemblies. Considering the sonic materiality of the crowd, I argue that the collection of voices that coalesce to produce the sound of the crowd can be understood through the sonic figure of the murmur. Drawing on Michel Serres’ formulation of noise, I suggest that the hum of a collective murmur foregrounds multiplicity and resists fixity. The murmur cannot be reduced to a singular voice or clean transmission but rather is always registered as a multiple. An attentiveness to the sonic dimension of the crowd allows us to develop an understanding of public assemblies as collectivities that enable and cultivate dissensus. I argue that the crowd can be read—or rather heard—as a social body that activates what Fred Moten and Stefano Harney refer to as an undercommon sociality. This paper proposes a form of micropolitical listening that attends to the materiality of a murmuring crowd and suggests that such an embodied listening practice might offer us a way to listen to a politics in process, a politics that is yet to cohere into a rigid and stratified form. Listening to the murmur of the crowd offers us a way of conceptualising collective politics anew.