Why do speakers make an odd noise when near a ringing phone?
Why do all speakers make the same odd noise when they are near a ringing phone & intercept the signal?
Dave - The phone is sending out a signal to all the nearby base stations, essentially telling them where it is, and I think possibly also to allow the base station to characterise what direction it should send the the signal in, and all sorts of other things like that. It does it just as it picks up a signal and also does it randomly during the day so that the base station knows where it is.
Chris - So you get an induced current in the speaker wire and off it goes!