Set some objects around you and observe bit weird sounding rain on vehicles.
- Legacy ID
This is not a bug, great video explanation though. I see exactly what you are talking about. The echo effect would be a simple fix. I will vote this up, even though I would never expect to see so many vehicles so close. Maybe the Devs could just use the "Louder" ambient rain for the inside of the vehicles only, or just at point blank range.
Just watched and listened to the video...
this is due to each helicopter emitting its own rain impact sound (which is good while stood still)
But ARMA 3's exaggerated 'doppler effect' as you're approaching one sample becomes higher in pitch (compressing the wavelength) than the sample that you're walking away from (stretching the wavelength) causing the two (or multiple in this case) wavelengths to go slightly out of phase.
resulting in the strange whooshing sound that you're hearing...
Maybe to fix this they could disable the Doppler effect for walking and running speeds as it isn't really noticeable in real life.