[DRG]

"Mystery solved". ( maybe.......) What version is your game?

The unit in the OOB is assigned sound 19 ( USMC unit 288 ) ... ALL small drones use that sound

Sound 19 is set up in the Sound.INI as "Drone19.WAV"

sound019="Drone19.WAV"

"Drone19.WAV" IS in the game and went in March 26 2022. I just checked my "virgin" game I use to check installers and it's there and sounds like a very large buzzing insect.

If you are using an older version of the game that 19 will set off " Null. wav" because sound 19 was not assigned before winSPMBT ver 16 any call for that sound will generate the " wonky Alien Zappy noise" ( "Null.WAV")

The only weird thing about this is you say they make that sound when they retreat....... 19 is the only sound they should be using forwards or backward

If you are up to date and you have checked your sound folder for 19 and 19 shows in Sound.ini then try to get a save game of this happening

EDIT FWIW I opened that scenario and pushed a small UAV over the lines and had it shot down..... no weird sound FX