A couple of people have mentioned the possibility that the speaker leads
could act as an antenna, and pick up unwanted radio signals. If you
consider that the output of an audio amp is very low impedance (8 ohms), it
would take a hugely strong radio field to generate any appreciable voltage
in that circuit. Secondly, it is hard for me to see how a radio frequency,
applied to the output circuit of an audio system could have any effect.