What’s going on inside all those disc drives, cellphones and computers?  We’ve grown accustomed to obvious sounds: the whirr of a burning disc, the start-ups and shut-downs, the overheating hum of internal fans.  But what about all the data stored, trashed and seemingly lost?  Detectives are able to recover data from hard drives, and even the Internet seems to keep a copy, as those who have tried to delete incriminating emails have discovered.  Digital footprints are nearly impervious to destruction, as Markus Mehr demonstrates via sharp amplification.  His induction microphones ferret out the hidden and over-written, exposing – and perhaps indicting – humanity’s newest enduring mark.