[SiriusHardware]

And one further thing - I transferred the modified file (18 seconds of audio tones but with a silent lead-in header) over to the little MP3 player and that now works, so clearly the problem there was that the player was making some kind of extraneous sound when waking up from being paused. The new 'silent header' provides a space in which to press 'Go' between the start-up thump/click and the beginning of the audio tones proper, so that was worth doing.