Precisely at 1800 UTC, a nasty 50-Hz hum appeared on the Buzzer signal. About half an hour prior to this, the strength of this signal dropped greatly.
Yes, 50 Hz is the power frequency in Russia.
It is definitely not a 60-Hz hum.
Someone else is sending VVVVVVVVV K in Morse, and of course the off-frequency air defense strings continue unabated.