Originally Posted By: tfabris
... My house, which is quite modern (built within the last 5-7 years or so) has always had a low frequency hum, at 60hz and at all the harmonic nodes above and below 60hz, which is so faint that I can only hear it when I'm scrutinizing the noise floor of things I've recorded with sensitive mics in my recording studio. I've never been able to track down its source...
Have you determined whether the recorded noise is accoustically induced or electrically coupled? If you enclose the microphone in accoustic absorbent material so the mic cannot 'hear' anything, does the recording still show the same amount of hum noise?

Do not use the microphone 'mute' switch for this test as this may alter the electrical properties of the microphone feed to the recording equipment.

Mechanically coupled noise can be weird to trace. Microphone mountings can conduct vibration into the mic from the surfaces the mic stand is attached to.