LOL, ran into that last year, had to replace it, now it is quieter but still certainly not silent. I'm trying to buy a big enough battery and inverter to shut it down during an outage, needs to run about a half hour. The inverter I bought and battery doesn't stay constant on, so I think the battery is still too small.
Actually, I think I need to replace the combustion fan. It is the one getting pretty loud. Or, at least buy one to have on hand when the one in the unit Sh#is the Bed.