how to get rid of video noise on my plasma????

when watching analog cable stations(especially lower freq. channels) my plasma has constant 2 inch wide bands moving slowly from top to bottom. no problem with digital stations or when watching dvd's. no audible noise. not much change at different times of the day. looks like 60hz video hum to me.what product do you recomend to cure this?
Jensen Transformer makes an in-line isolator that I have used to get rid of video ground loops. Good luck.