I have a Carrier Weather-Maker furnace. It is a model 58sxc high eff. unit. The problem I'm having is that when the burners come on, there is a kind of fluttering, whisteling sound coming from in behind the draft inducer housing. I have removed the whole motor and wheel assbly. and have found nothing. All the water drains are free and clear as well as the flame looks fine. Do you think it may be a cracked heat exchanger? The unit is about 10 years old.