The squirrel cage fan in my Regency warmhearth occasionally gets a little noisy, and I pull it out and clean and lubricate it periodically. It is mounted on piece of thick sheet metal, which is normally wedged under some metal flaps, but I found that I can find a better position for it that results in much less resonance. The improvement is significant. I'll see if it migrates around down there, but so far it seems to be staying in place. So, if your fan rumbles, you might try this.