This was reported as a bug few times, and was partially fixed couple months ago, but I want to say this is a feature, not bug.
Remember the scene from “Interstellar” (https://www.youtube.com/watch?v=bmz9lMP6aQU) where little girl says “let it go” referring to shut down drone as if it was a living creature.
When a destroyed hunter produces sounds it reminds me that scene and strikes with empathy to the poor guy. All the motor functions and hydraulics may be destroyed, but the electronics and sensors may still be running on backup battery (or even a separate power system, which is not uncommon in remote controlled models, for example). Depending on how you’ve destroyed them it might be possible they still see you, but can’t move or shoot.