331 000, heard on the Hong Kong websdr on globaltuners.
The call was 661, not 331. As it was a null message it was "661 661 661 000" repeated for 2 minutes.
Frequency was 16037 kHz at 0300 UTC, and 14637 kHz at 0320 UTC. Since it was a null the third transmission, 12137 kHz at 0340 UTC, did not happen.
T!