Recently I've been getting a low vibration/buzz noise from the handler unit that is located in a closet in my condo. When that sound happens I also get the same noise from my circuit breaker box. I am not sure if this is just vibration carrying through the walls or an actual electrical issue. If I press the box frame against the wall the sound in the box subsides, so I'm inclined to believe it's traveling vibrations.
This morning the unit was making a very loud vibration/buzz noise, which of course carried into the breaker box. The unit was not running and the sound seemed to emanate from where the copper tubing leaves the unit and runs into the attic to what I assume is the AC unit on the roof. Eventually the sound subsided.
I'm not sure how old the unit is as it has been there since I moved in 6 years ago.