I can hear movement on the mic - but it still squeals - no audible sound - bad mic - bad camera?
High pitched "squeal", and not a hum or buzz, correct? What do you mean "you can hear movement on the mike" but "no audible sound"?
IMHO a hum or buzz would indicate an open ground on the audio line. Since you describe a "squeal" my guess would be bad camera.
Does the camera give you good video? Have you tried some other audio source to your monitor to verify it is OK? I think the SC23A uses twisted pair in the camera cable so it should be immune to picking up stray signal, but is there any way you can move the cable around while listening to the monitor? Changes in the sound could indicate the squeal is being inductively coupled into the long camera cable. Don't run the camera cable parallel to other cables. If you have to, try and maintain a separation of a foot or more between parallel cables.