I would like some advice regarding our gas furnace. Lately just before the furnace comes on you can hear a thumping clicking noise. Actually only happens about 3 to 4 times a day. We had a repariman at the house last winter to fix the furnace since the starter needed to be replaced. Furnace is only 12 years old. Is this something dangerous if we choose to ignore. What can we do to remedy the noise. Thanks so much