Sometimes old faulty CRT monitors generate nasty high-frequency squeal sound. What element might be responsible for generating such sound? I have heard that it might be dry electrolytic capacitor; is it? What is the physics of generating this sound (how it is generated)?
Such noise is generated by the so called "line" (= horizontal deflection or flyback) transformer. This transformer does several things in a CRT or TV at the same time: it couples the horizontal output stage to the horizontal deflection coils and recovers the energy from the coils field during flyback, and generates the high voltage for the CRT (about 20 kV).
The transformer has a core made from ferrite material. Such materials have a small and unwanted magnetostriction effect (There a varieties of ferrites which have a strong effect). In case of failiure the core of such a transformer can be driven into saturation, and the frequency of oscillation comes down to the region where our ears are much more sensitive. Then You hear that vibration of the core.
BTW in the 50ties, when I was much younger (including my ears) I could hear the 15 625 Hz tone of TV sets out in the street when I passed houses at nighttime (less other noise). Whether the transformers were louder in those times, or I just had better ears, I don't know.
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its down to the pizza-electric effect where faulty electric signals in the audio range cause components to wiggle mechanically in the audio range.