999 kHz радио россии.
On 999 kHz is Radio Rossii (Russia’s radio). This forum reported it, I can confirm that.
Maybe it comes from маяк (Majak), there 999 is being used for other broadcasters and Russia also rents airtime for 1413 there.
Yesterday there were also test transmissions with piano music from Russia on 11710 kHz. Maybe Russia plans to come back to the AM bands.