"transmitting" as in actually sending data, or just the radio left on, set by default to the lowest channel, and transmitting an otherwise useless carrier wave?
Transmitting with a blank SSID apparently. It just adds to the congestion on 2.4 GHz for no reason. For myself, it interferes with my wireless development activities. See this thread on the Comcast forum where folks are seeing all sorts of bad behavior.
http://forums.xfinity.com/t5/Home-Networking-Router-WiFi/Xfi...