Like most bits of tat owned by HMFC, one of the fridges at a certain medical centre developed a fault. A 50 Hz mains hum buzzed over the headphones - but stopped whenever it was supposed to go 'beep'. Aircrew being aircrew, no-one mentioned it and months went by with aircrew of all ages getting astonishingly good results.....
PS - Surely the quacks must know that most things have volume controls?
PPS- Is it still A E C O N H T L on the bottom of the eye chart?