[drh4683]

I don't know if I would suspect mechanical flyback vibration just yet. Does the picture seem stable? Do you see jittering in the picture when you hear the noise? If so, then yes, you do have a vibrating flyback or you have HV leakage somewhere within the HV cage (the metal compartment on the right side of the chassis). Id be willing to bet you have a microphonic horizontal output tube. Some sets will make an unusual loud ringing noise when the elements in the horizontal output tube are loose. That set uses a 6LB6 horizontal output tube. Loose elements will vibrate at the horizontal sweep frequency and cause some weirdo sounds that are quite loud. Ive experience it before on my 20X1C38 console. The sound will change pitch and sometimes go away for a moment. This symptom will not cause picture jittering or distortion. While the set is on, take the eraser end of a pencil and tap the 6LB6 and see if you have any change in pitch. You can also take the tube out of the set and tap it and listen for loose elements. You will hear alot of ringing and jittering if the tube is bad (all tubes have this to a certian extent but some are alot worse than others) I have found RCA horizontal outputs to be worse than any other brand for this problem. I mainly only use GE, Sylvania or Zenith replacement tubes in all my sets.
But like I say, first check to make sure you don't have any picture jittering accompanying the sound, as mechanical vibration will almost always be noted on the screen. (picture jittering on the screen caused by flyback or HV leakage is called "piecrust effect" as a round shape will look like a pie crust if the problem exists)