The helicopter passed overhead with a ... sound, like a giant insect.

Onomatopoeia (অনুকার শব্দ): A word that phonetically imitates, resembles or suggests the source of the sound that it describes. Example-miaow, roar, cuckoo etc. (এক ধরণের শব্দ যা কোন প্রাণী বা কোন কিছুর আওয়াজ থেকে উৎপন্ন হয়)। A figure of speech in which the sound of words and phrases suggests the sense.

For example:

• "Chug, chug, chug. Puff, puff, puff. Ding-dong, ding-dong. The little train rumbled over the tracks."("Watty Piper" [Arnold Munk], The Little Engine That Could)
• "Plop, plop, fizz, fizz, oh what a relief it is." (Slogan of Alka Seltzer, U.S.)
• The buzzing bee flew away.
• The sack fell into the river with a splash.
• The books fell on the table with a loud thump.
• He looked at the roaring sky.
• The rustling leaves kept me awake.
• The sheep went, “Baa.”
• The best part about music class is that you can bang on the drum.
• It is not unusual for a dog to bark when visitors arrive.