That ringing noise sounds like a deflection yolk or an on board coil is starting to sing as we call it. theres not alot you can do unless you find the source as the deflection yolf in the past we used to stick popcycle sticks into the yolk while in place and hot clue them to get rid of singing yolks.. But its onlty a temp fix. the best way to fix it is too replace the singing yolk. Now if its a coil it could be a loose winding on the coil and hot clueing the coil on the outside sometimes fixes thast too but in the end the best way was to replace the coil that makes noise.
What you are hearing is probably the Horizontal oscillator @ 15,750 Hz. Most common offender of this is the High Voltage xformer , sometimes you can wedge something in it to make ot stop. It could also be the yoke as in the previouse reply. 25,000 volts there, be very carefull. Hope this helps.
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