I recently noticed my furnace making a buzzing/humming noise (similar to a 60 Hz noise hum...) all the time.
It does this even when off / not running. My fiancee says it's always done that, but I've never noticed it. It's loud enough that I can hear it upstairs (main floor) through the vents when the house is quiet.
Anyone know if it's normal and/or what it could be?