So, fired up furnace first time this season. Yeah, we live in Central Texas...
After a few moments of fan only, as I stand outside by the furnace,5 "woosh", I get the sound of the furnace burner coming to life!
I see 3 small embers come out after about a minute... Then two more about a minute apart. Then they stop coming and things are merrily humming.
I find my way inside... Warming nicely!!! After running about 7-8 minutes, I notice a "rumble"...hmmmm was that there before? It is a different harmonic.. Not scraping, not metallic... Just a rumble... All appears fine... System cycles and when fan runs I have slight rumble.
It doesn't set your teeth on edge... Just rumbles...
I did not see any debris or mud dauber residue on fan blades...
So.... Any thoughts other than "turn up the radio"?
Peace and Blessings..