Q: What is that combination of buzzing and Morse code-like sounds which seem to emanate from my cell phone when I'm around electromagnetic equipment?
A: My son, that is the sound of a cell phone "checking in" with the nearest cell tower.
Cell phones and towers communicate back and forth at times so that each knows that the other one is there (in simplest terms). That sound that you're hearing is the phone's end of that communication.
You'll often hear that familiar buzzing and Morse code-like interference when your phone is near a radio (especially AM), a television, the pick-ups on an electric guitar or an amplifier of some sort. Anything electromagnetic. Ya heard?
To produce sound, an electric guitar senses the vibrations of the strings electronically and routes an electronic signal to an amplifier and speaker. The sensing occurs in a magnetic pickup mounted under the strings on the guitar's body.
This pickup consists of a bar magnet wrapped with as many as 7,000 turns of fine wire. If you have read How Electromagnets Work, then you know that coils and magnets can turn electrical energy into motion. In the same way, they can turn motion into electrical energy. In the case of an electric guitar, the vibrating steel strings produce a corresponding vibration in the magnet's magnetic field and therefore a vibrating current in the coil.