Hearing a new noise coming from our furnace.. It sounds like a helicopter, low whine/buzz/vibration coming through the duct work. I turned on just the summer fan and no unusual noise so am I on the right track thinking it may be the combustion/inducer fan? I have not looked at it yet, need some help and it is in an awkward place, the attic, but wanted to get a feel about what I should be looking for/at.