here are various high frequency dog whistle hums, from #1 to #8. Do any resemble what you heard?
1:10 sec. ttl
https://www.youtube.com/watch?v=8oWaYF1MpGI
Sound Experiment - Dog Whistle
Umm ... If I were a dog I could hear them all, but alas I’m not. Those are whistles not ‘hums’. The Hum is supposed to be 30-40hz range. Some say is earthquake generated - I have no idea if that’s true or not.
Russian Woodpecker sound
Russian Military voice in clear - you can hear one guy reading off a 5 day pad
https://www.youtube.com/watch?v=jkB5rZRBPWk
Tank traffic was in the 5 hz range - the above sounds like regular traffic between troop units.
There don’t seem to be any recordings of the sound you’d hear without breaking the PPM signal out into separate channels. I do remember there is a timing pulse (sort of like ding ding ding ding) repeated between on set of traffic and another until new traffic transmitted. I cannot write what it sounded like - a jumble of sound clicks buzzes hums dings all intermixed.
It is possible to hand wind copper to the right freqs to break all that out, but you’d have to know it was there in the first place - plus most of what you’d get is encrypted. Only once in a while there would be a high level voice communication on one channel - which was supposed to be for maintenance - but the generals and politicians seemed to disregard that