residual hum

例句：

1. 1. The old building still has a residual hum from the old air conditioning system.
   这座旧建筑仍然有来自旧空调系统的残余嗡嗡声。
2. 2.The hum of traffic in the city is a constant reminder of the busy life.
   城市中交通的嗡嗡声是忙碌生活的不断提醒。
3. 3.The residual hum was so faint that it could barely be heard over the background noise.
   残留的嗡嗡声非常微弱，以至于在背景噪音中几乎听不见。