In rec.radio.shortwave on Tue, 16 Sep 2003 15:38:24 -0500,
"Clifton T. Sharp Jr." wrote:

Funny you should use that comparison. The first time I ever listened to
SW was at the house of a friend who had just got the radio and didn't
know a thing about it. Not knowing about Soviet jamming stations, every
time we passed one all we could imagine was that it was ignition noise
from a propellor airplane somewhere. This was waaay back in the day of
the buzzsaw and before sophisticated jammers like bubble jammers.

The "open mike in an airplane cockpit" sound, when found in the middle of the
ute bands, is actually multi-channel teletype. If you can find one of them,
and if you have a sufficiently narrow filter, you can pull individual channels
out and hear very narrow shift FSK.

Those of us who were SWLs and who worked on AN/TCC-4 TT multiplex equipment in
the military all had "aha, that's what that is" moments the first time we
listened to a carrier channel that had one of these connected to it.