OK guys - another strange noise - and I finally tracked it down..
A funny "buzz" sound - definitely electrical. On the ground floor it sounded downstairs, in the basement it sounded up-stairs. Not in the closet, not out of the fuse box.
Attached to a floor joist in the basement, behind a cabinet - is a small square metal box, romex cable in and out and a small wire running across the joist and into the oil burner. Apparently it is some kind of transformer.
The thing is - maybe because it is the summer and nobody is around: But I never heard this thing for years and now I hear it all the time.. It looks original to the house (early '50s). Could this thing be breaking down? Is this noise normal? Is it a potential fire hazard?
Thanks.