Mark, you can check your heat outlet in the bay. The tin foil pipe vent in compartment, third one to the rear from LP gas tank, about a foot back from outlet you will see fan motor that cycles with furnace on and off if your switch is on in water bay. You may have something caught in fan, I had a mouse macerated
in the barrel fan of furnace made for a loud squeel
when it happened and fried remains on burner tubes. Scared the he!!! out of wife an sister inlaw. One could be setting up shop in tube or you may have crushed something against tube, don't see how fan is protected by metal plates on either side.