I think perhaps the noise made by bots - especially the huge walker bots - exploding should probably travel a larger radius. Bit of a spoiler on the final fight below.
I had the final fight with Plutonia, who was surrounded by a Tank, who was next to a big walker bot and a medbot. Nobody noticed my silently taking the medbot apart, but the walker bot woke up when he exploded. The Tank didn’t hear nuttin’. I emped the walker and slowly whittled away at him with my EMP-modded silent weapons until he exploded in his huge explosion. Tank and Plutonia and the Hunter further away still not heard nuttin’. And that Tank’s circle was just barely outside the walker bot. If I had fired a gun from further away at the first medbot, you can be sure they would have heard me!