Screaming Picture Tube???

I got a 12" B/W Zenith portable. Looks from the 50's or 60's. No picture. Loud squealing noise that seems to be coming from the pciture tube. I hear it even with the volume down. When I turn up the volume I hear it through the speaker (picking up the frequency I guess) and hum through the speaker when I turn it up more. But when I turn the volume down all the way this loud screaming noise remains. And I mean it is LOUD! I have never had anything like this happen and am kind of afraid to work on it now. Any help would be much appreciated. Thanks in advance!