Has anyone insulated to cut down on furnace noise?

In my experiece with a home gas furnace (high efficiency with exhaust through a plastic pipe) the fan squealing is due to lack if lubrication. Mine had oil embedded in the plastic and was supposed to keep the bearing oiled for years. It did for 5 years. I stopped the squeal by oiling the bearing but the quiet only lasted a few days. It wasn't made to be oiled! I bought a new fan just to get a new 5 year supply of convenient oil. I did keep the old one as a spare for emergency use.