We had a power outage for about 45 minutes. Had at least a dozen of them over the years.
When the power came back on my TV was making a sound. I unplugged it and plugged back in and still the same sound.
I unplugged it again and waited 30 minutes and plugged it in.
I get the same sound you can hear in this audio file.
The sound occurs with the TV off and the TV will not come on via the power swtich or the cable TV switch.