"The Coast Guard uses AES encryption on the digital channels."
That may be so in Washington but not in central NJ. The "digital channels" here are non-encrypted P25 yet any other normally analog channel may be digital AES encrypted at times. I have heard it often enough sounding like a rough hiss so like the commercial goes; "your actual mileage may vary".
I wish they'd go back to teaching circuits and theory to radio operators, unfortunately training how to use a radio says nothing about how it works. FYI, you cannot hear an unmodulated carrier, if there is nothing to demodulate there is nothing to hear. Conversely, be it analog or digital, encrypted or clear you'll hear modulation of some sort if there is any. We're not talking Coast Guard radios here which apparently mute the audio unless decryption is enabled, try listening on a scanner and you'll hear what it actually sounds like on air.