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WiFi or cell phone signals are way to fast for you to hear individual dits and dahs, and they don't use that kind of encoding anyway.

What you are hearing is the carrier from a local ham operator sending morse code getting unintentionally detected by the electronics in your sound system.  This ham operator is nearby, so the signal quite strong.  

The morse code is carried by the carrier being keyed on and off.  There is otherwise no modulation, like voice.  One of the more sensitive circuits in your audio system is picking up enough of this carrier for the result to be audible when it gets switched on and off.

No system is totally immune to interference from external radio signals, especially strong ones from a ham operator next door.  It costs money to make circuits less susceptible, so consumer electronics only does so just enough to not pick up normal radio stations.  If you lived next door to an AM commercial radio station transmitter, you'd probably hear interference too.

Better equipment that is less susceptible would fix the problem, but that would also likely make it more expensive and it's hard to know how susceptible something is until you try it.  This is not something usually specified, especially for consumer gear where the average customer buys on price and can't spell "RF" anyway.

You could try putting some aluminum foil around the speaker box containing the amplifier, connecting the foil to the ground of the audio input right where the cable enters the box.