Do you have a language, time in UTC and mode? On 6.661MHz USB I hear airline traffic from India and other parts of Asia. So being on 6.664MHz are very close to aircraft channels.
The language may be the key to solving this one and the time you heard it in UTC.
The 4-10MHz section of HF is populated by illegal stations in this region, especially from Indonesia, Philippines, China and Burma etc. The Indonesian offenders are illegal "village radio" CB style stations.
All probably intermingled with illegal fishing vessels too.

In the interim, will have a listen there from time to time...
