Atwood Furnace Squeals

My '96 Pace Arrow has the original Atwood LP furnace. Because of LP prices we only use for back up at night to keep pipes from freezing. We use electric ceramic heaters for heat during the day if needed. It has developed a loud squeal when the fan starts before the burner has ignited. After it runs 5-10 seconds it goes away. If it runs often enough it doesn't do it always or as bad upon subsequent firings. The owner's manual says the bearings are sealed and lifetime. Is there a way to access a place to try to lube them. After looking at the furnace from the outside removing the furnace would be difficult at best due to it being riveted in place. On the inside you can only see the manifold for the ductwork so that is of no help.
THANKS!