Four-cylinder 2 stroke engines running flat out and then some, make a lot of noise. At $10K a pop they are cheaper than some artillery rounds and unless GPS jammed, are as accurate as a precision weapon just by using commercial GPS service.
'They Sound Like Motorbikes': Ukrainians Say They Can Hear Iranian Suicide Drones Coming
362,864 views Oct 7, 2022 Russia has resorted to using Shahed-136 drones from Iran in its war on Ukraine. Ukraine says it's already downed many of the drones, which work by slamming into their intended target, laden with explosives. Ordinary Ukrainians say they can already recognize the sound of the drones.