flapping sound (of wings); fluttering; hum (of insects); buzz (of bees, etc.)
whizz (of a flying arrow); whoosh
蚊の羽音で目が覚めた。
I woke up to the sound of a mosquito buzzing.
蝉の羽音が夏の訪れを告げる。
The sound of cicada wings announces the arrival of summer.
羽音を立てずに飛ぶ蝶がいる。
There are butterflies that fly without making a sound.