Signal noisy is a relative term. Nanites would use spread-spectrum synchronized pulses for directional broadcasting. Command signals after release are encrypted and encoded.
It’ll be like electroshock therapy to the heart. First you administer the shock, then you take advantage of their confusion as they attempt to reestablish communication to decrypt their codes.
Then you rewrite their programming or shut them down.
Could probably use that to track down the initiating Slaver as well.
It likely would have to be relatively nearby to keep communication stable with the nanites, and likely would use the slaved hordes it controls to overwhelm defenders preperatory to adding them to the hordes.
Which it would have to do itself, exposing it to attack.