Hum Created When lav mic connect to jack

Using a Toshiba Camileo X200, I'm getting a humming sound like a motor running while using an audio-technica ATR3350 lav mic. I checked the mic itself on another device and there was no hum, so I'm assuming the jack or camcorder is the root of the problem. The camcorder works fine from its own internal mic, but when I plugin the mic, the recording reveals the hum....even without the mic being turned on! It makes no difference whether or not the mic is turned on, the hum remains present with no change.

The mic has a stereo jack, but I cannot find spec info about the camcorder receptacle.

Any suggestions are appreciated.