I had the exact same thing!

http://www.doityourself.com/forum/el...ml#post2228215


My breaker for the furnace was buzzing, the furnace was not running so I flipped the switch - no more buzz. Then a few days later the buzz was so loud it woke me up!! (panel is in my walk-in closet). Since the furnace was running this time I just pushed hard on the breaker and it quit......that was about a week ago - no more buzzing since. My furnace has taken a beating this winter (brrrrr it's cold in SC) so I thought the breaker and furnace didn't know what the heck was going on since in a normal winter we rarely run the furnace all winter. Serious note, I am concerned about it - should I have a electrician look at it?

 

Is that a walk-in clothes closet, as in a bedroom?

I would if I were you, just to be on the safe side.