In old televisions with a cathode ray tube (kinescope), the image was displayed in frames of 25 frames per second. Each frame was drawn in lines with a frequency of 15625 hertz, i.e. slightly over 15 kilohertz. A voltage of this frequency was supplied from a horizontal scan generator to the horizontal deflection coils. Some of the radio elements of the horizontal scanning unit (horizontal transformer, coils) vibrated slightly at this frequency, creating a faint sound. The frequency of 15 kilohertz (thin squeak) is close to the maximum perceived by the human ear, it is well heard by children and young people, and, as a rule, middle-aged and elderly people do not hear it. You hear, your hearing is okay.
I will assume that you are the youngest in the family - hearing deteriorates with age. The perception of high frequencies is especially strongly reduced, and often already by the age of 30. You can test yourself and other family members here - www.noiseaddicts.com. High frequencies are also extremely unpleasant to the ear, and the sound of an old TV is just that high-frequency.