could be the ignition system
I was in the basement this morning doing some laundry when my oil furnace kicked on but before it did there was a buzzing sound for about five seconds before it started. Once it started everything sounded fine but the buzzing has me a bit concerned. For all I know it could do this all the time and I just never noticed. I'm going to check if this replicates itself when I get home from work but is this something someone should take a look at?
could be the ignition system