I've tried listening with my ear up to the hive but that darn ringing makes it difficult.
Grabbed a stethoscope from my trauma bag and voila, a tap on the side of the hive and they're a-buzzin'.
Out of 4.5 hives, two are quieter than the others already.
i like doing that too. if you move the stethoscope to different spots, you can sort of figure out what part of the box they are in.
the other cool thing is during mating season, when you can hear several virgins piping back and forth in the same hive.