I called Zone Defense and left a message. A tech guy called me back. He said there is a pin hole in the back of the camera. As I suspected, he suspects too, the pin hole is clogged with dirt or other foreign matter. I'll have to dismount it to clean the hole. Then hopefully I'll have sound again.
I also asked about the LEDs. He says they are IR LEDs. The naked eye won't see the light, but the camera picks up the images in the dark. That explains how I could see in the monitor, my wife walking around behind the rig in the dark.
