A mutter of complaint spread through the office when overtime was announced.

宣布要加班時，辦公室裡傳出一陣抱怨的嘟囔聲。

The passengers gave an annoyed mutter as the flight delay was posted again.

航班延誤的消息再次公告時，乘客們不滿地低聲發牢騷。

I heard a low mutter from the customer waiting at the service counter.

我聽到在服務櫃檯等候的顧客低聲嘟囔著。