The horizontal circuit opereates at a frequency of about 16kHz, when components start vibrating at the frequency, some folks can hear it. That MAY be what you are hearing.
An old car mechanic taught me a trick about 60 years ago that he used to track down where a strange sound might be coming from, and I have used it in electronics work since the 60s. You'll need an old wooden dowel, spoon, or drumstick. One that is long enough that you don't stick your head too close to things that might hurt you. Now, place one end of the spoon on the suspect components and the other end at the entrance to your ear canal. Where you hear the loudest sound is likely the source. In your case, try the horizontal driver and flyback transformers, width coil, and even the deflection yoke. If there are any ferrite beads on component leads in the horizontal circuit, they may also be suspects, but the sound will stop when you touch them.
Best of luck tracking this down. That sound can be very aggravating to some folks.
