I have a vibraton in furnace only when flame is lit. Blower motor seems fine. Is this vibration normal? Recently replaced inducer motor. Heat exchanger has been replaced once. Does not appear to be any cracks or orange flame. Does not do this when A/C runs only when furnace runs. Any ideas?
I'd suspect the new inducer (exhaust) motor if this sound begins to occur just before ignition; before the HSI ( hot surface ignitor) gets hot. A gas flame makes more of a roar than a hum. I've had less than stellar inducer motors in the past, with questionable bearings making it sound like rum-rum-rum-rum...
I've also had duct work vibrate at the unit; go around putting pressure on things until the sound changes. I still believe the sound is caused by the inducer; though it's not necessarily the source of the sound.
Take the furnace's top-section of the faceplate off, and try grabbing stuff; beware the 120v wiring. Tighten down the clamps that lead from inducer motor to the plastic pipe. Also try putting little pieces of insulation where piping might be resting on things.
It's not unheard of that replacement parts be less than spectacular. Encountering this exact problem, I've lived with a (now a little less) noisy replacement inducer for 10 years now.
I would first fully inspect the exhaust for obstructions.
It is quite possible that in the process of combustion, pressure is building inside the heat exchanger, and then having difficulty moving through the appliance to eventually exhaust.
The inducer is designed to help overcome this.
Basically, what happens is that the combustion pressure overcomes the ability of the fan. Some "slippage" over the fan tips will occur and the fan catches up. Left alone, this can cause a noticeable rumble that is methodical.
Spelling may be incorrect, but it is called the heimheld effect (I am a combustion guy).
Look for obstructions in the flue...excessive flue lengths.
Call the OEM tech line, or search boards "specifically" for your model. Tech lines are VERY helpful, if you accurately describe the issue.
As someone not in the industry, you may not get to them easily...but being polite will open a lot of doors.
Maybe start with the local sales rep in your area...he will have a guy on speed dial..and you might just remember him when it comes time to replace!