Scrolling through various shortwave frequencies, caught couple tones among the noise. Sounded like sad horns. Radio used was a grundig yacht boy 207 with a broken antenna, recorded on a tascam dr-05x.
A sound stimuli to demonstrate combination tone from speakers. You should hear additional frequency of 500 hz. The sound itself is summation of1000 hz and 1500 hz.
This tone was generated using audacity. In the base there is a 45hz sinusoid. Then a new sinusoid tone of 207hz is added for about 5s. After a pause of about 5s a second sinusoid of 208hz is added for 5s.