Lewis & Short

ad-murmŭro, āvi, ātum, 1, v. n., to murmur with approbation or disapprobation (cf. acclamo): quam valde universi admurmurārint, Cic. Verr. 2, 5, 16: admurmurante senatu neque me invito, id. Att. 1, 13, 2.
Impers.: cum esset admurmuratum, Cic. de Or. 2, 70, 285.