When I was in the Air Force as a comm tech, they used to run 13, 16, and 22 channels of teletype (60-100 Baud) multiplexed together and shot out over a voice channel over some comm link (long haul multi-hop HF, VHF, UHF, and MW.
As they were staggered in frequency up conversion and multiplexed together to be sent out over a 3kHz voice channel, the sound was exactly like a 4 engine propeller airplane - exactly. If you tuned in on HF bands, you’ve likely run across this if you’re old as I am.
We had an old stand up cabinet radio in the basement when we were kids. Tuning across SW we would hear those buzzing and roaring sounds and didn't know whar they were. My best friend [at 14 y o] solemnly announced that noise must be coming from the hydroelectric plant cause nothing else could be that powerful.....(:}