Sizzling noise at the same time so probably voltages of 50 volt or less.
Cracking noise would be higher voltage area.
Sometime I'll take the cover off and trace the dry joint/loose wire.

Probably dirt and grime in the monitor.

In my case, I upgraded the BIOS in my mainboard.

Since I had other problems in addition to this associated with the BIOS
upgrade, I flashed back to my previous BIOS verson and the problem went away.

This may or may not be the case for this particular instance, but you can't
rule it out without troubleshooting. - Reinhart