I have an older (10-15 years) Magnavox 19" color TV that is serving me
well. Recently, however, it has developed a sort of nervous tic.
Something within it is vibrating enough that it produces a noticeable
buzzing noise. If I put a dictionary on top of it, the housing is
damped enough to kill the noise, if not the source of the vibration.

When it does appear, the set has always been on for at least an hour.
But it does not always appear when the set has been on. Somewhat
unexpectedly, if the television is turned off, it takes perhaps 15
minutes to stop vibrating.

Does anyone have any speculations about cause and/or remedy?

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Thank you for your comments and consideration.