Tv rings After turning on tv for a couple of minutes a high pich ringing starts

In these sets, I have found that the squealing is caused by the horizontal transformer. It is caused by a part (usually a coil or transformer that is vibrating).
My shop will take a pencil ( with eraser) and just barely touch ( with the eraser side) the component that we think is making the noise. If the pitch changes or goes away completely then that is the part that is making the noise. If not, then we move on to the next suspected part.
When the part is found, unplug the set and apply a solution around the coil or transformer. The solution we use is fingernail polish ( I know, we are professionals, but, it has worked for us over 35 years). Let it dry, about 10 to 15 minutes.
When trying to detect the noise, the set must be running, do not put both hands inside the set at the same time and do not touch any part of the ground with that second hand.
Any questions, respond to this post and I will respond.