As the title says, even if you turn the engine off and disassemble it, you hear the still hear it. However if you assemble it again it will appear with running engines (or if you turned off the engine, it will be "shutting down" state)
The problem, when you disassemble it while its engine running and then you assemble it again and the UAV is the same state (engine on / shutting down) is a bug previous Arma 3 builds already had. The new thing is the sound being stuck.
See video: http://youtu.be/z3ZSCZQRMGM
- UAV instantly shuts down if you disassemble it, if you assemble it again its engine will be off.
- You restrict disassembling UAVs until they are shut down completely.