You'll hear the music not only when you're near the hot lead of a 70V signal, but if the wire is small in gauge (say 18 or smaller) you might even hear the music on the ground because of the resistance of the wire. Ask if you need an explanation.

It's not good practice to run data and audio next to one another, but mostly low level audio and data, because data can leak into the audio cable. That's the reverse of the problem you fear.

You're not likely to have a data problem. See, you're not measuring for audio on the data wire when the data wire is connected. Connecting adjacent wires to ground or to the equipment they normally go to will greatly reduce the amount of music you hear when you're near the speaker wires. Toners spray an electric field all over the place and nearby grounding lessens it.