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Can you give me complete model from inside furnace in burner compartment so I can provide guidance with this specific unit.Model will be on a label just above burners on right or left inside panel
Listen and tell me if the whistling seems to be coming from the small vent fan where vent connects..
Then look in blower compartment and see if we have a control board with a blinking light.If so tell me the pattern of that flash.That will indicate what is wrong and tell us where to start troubleshooting.