Monitor making noise

I'm not certain, but perhaps it has something to do with the location of the monitors, maybe theres a magnetic disturbance naturally occuring wherever it happens to be. I have two monitors in two separate rooms about ten or fifteen feet apart, and both of them make noise periodically. Almost like a whistle. I'm way out in the boonies, and there are hundreds of feet between this house and the next. I've been loosely reading about RFID's and their interference by a Faraday Cage effect, perhaps something like that is interfering with the electronics inside of the monitors. This problem is most apparent in CRD monitors, as I've never experienced it with an LCD or anything else. Just a thought.