There appears to be a poltergeist in my speakers (no, really)

It's not a new problem: PC speakers also pick up radio

This seems to be a common example (to judge by a Google search) of radio frequency interference or RFI, though it's not something I've heard on a PC. The speaker wires may be acting as an aerial and picking up a radio signal, which you then hear from the speakers. The loudspeakers may also be implicated: some models seem to have better shielding than others.

You could try moving the speaker and mains cables, and folding up (rather than coiling up) any spare bits of wire, or changing to shorter, better-quality shielded speaker cables. If that doesn't work, try adding some ferrite rings to the speaker and mains cables. [...]

Basically your speaker cables work as an antenna and picks up normal radio.

Chances are that something is picking up a radio station through another channel somewhere and the speakers just amplify the signal. This is actually quite common.

Your speakers are acting as a basic radio. What you need to do is use grounded outlets. This will typically fix your problem.

One of your cables is acting like an antenna. Get some of the various "ties" (used to keep your cables untangled) and tie up/bundle each of the cables. I was picking up some Mexican station and this worked for me. Apparently, this "shortened" cable then does not act like an antenna and pick up the radio stations.