I have original gas Interthem furnace in my 1972 mobile home and do best to keep it serviced and clean. This morning furnace began to squeel, but only when heat turned on, not if just the blower is on. Just cleaned door filter & vacuumed around fan blades, put 10 drops correct oil in the place for the motor oil. It sounds like from blower assembly, but?? Help! It's cold in Idaho and I'm afraid to run the furnace, but even more afraid to call for heating company for help - Thank you ~ Freida in Idaho