It’s the one part of the radio spectrum that’s also in the hearing range hence induced currents from it can be heard in an analog audio system and which would have a pretty decent amount of energy inside a building because it’s being emitted pretty much all around by the mains power wires.

That said, you’re right that depending on the length and shape those wire might not be a very good antenna for that frequency. Independently of that, I doubt there’s enough energy around to directly affect speakers, but it might be enough if that wire goes to an amplifier and only afterwards to the speakes.

That said, I’m from Digital Systems rather than Telecomms or Audio so take what I say on this as a semi-informed guess.