It would have to be the call centre music used by both the National Insurance and Pensions help lines. Two alternating tunes that drive you so crazy that you (sorry, I) begin to imagine a band in a little studio playing them over and over in real time, with a conductor that halts them at random intervals so the mic can be passed to someone who intones 'did you know the answers to many questions can be found on our website?' or 'we are a diverse group and abuse of any kind will not be tolerated' or 'you are moving forward in the queue. Your position is currently...' - the mic is then passed onto someone with an almost but not quite similar voice, who utters a random but always increasing number.