Got a 20 year old Trane XL90 furnace which is having issues. The exact moment it goes on, a very loud humming/grinding noise comes on. It gets a bit softer after the first 10 to 20 seconds of being on, but its still loud enough to hear from the next floor up.
I know for a fact its coming from the inducer valve and inducer motor region but I'm having a hard time determining which one is the culprit. Trying to save some $$$ here to replace either the valve or the motor, if thats possible.
I had a similar problem with my comfortmaker enviro-plus 90. It was the inducer fan. The fan wheel hub had cracked and was running unbalanced. Of course I could not just buy the wheel I had to buy the whole fan and motor. Hope this helps.