Within the past 2 months, the blower to my furnace has developed a whistle. It's not terrible yet, but appears to be getting worse. I have changed filters, etc...I have listened with my ear, the whistle is primarily generated inside the furnace itself by the blower. It seems to get worse once the burner turns off and it's in the final 2 minutes of a cycle.
any thoughts? Dust inside? Is there regular maintanance to the blower motor necessary? The plate on the outside says no lubrication is necessary. I have a 3 year old Carrier Oil fired Hot Air furnace.