Out in the battlefield that you suggest using the drone in, it will be very quiet. No lights, no vehicles moving around, just soldiers on watch for the night, listening for those pesky drones that everyone seems so fond of using.I'm surprised how quiet drones are. Out in the battlefield there's no lights. Are you going to turn on a flash light to see to expose yourself? Like I said before if you watch video of homemade suicide drones at work and the enemy doesn't notice them until it's too late and it's out in the daylight. Again Hezbollah flew drones over Israeli strategic areas without being discovered until is was posted on the internet. Don't you think the Israelis would have the technology to detect them? It just shows you how there's a lot assumptions about warfare that are not true. Who would've thought an M1 Abrams can be destroyed by essentially is a toy drone. Drones have completely change the battlefield and how people see it. One would think drones can easily be countered but apparently they're not. Nearly all anti-drone tech requires something to be aimed at the drone to make it work. At night you don't know where it is.
The noise of drones that can carry and aim a rifle will be much louder than the noise of a drone that carries a kilogram of explosive. Rifle is heavier, larger, and more cumbersome than a little chunk of C4.
I guarantee that you try and stealthily fly a drone carrying a rifle within 20 meters of an alert sentry, they will hear the approach.