We have a hot air furnace that is making a terrible growling sound when the fan comes on. We cannot isolate where it is coming from. If you put your ear to the fuel lines, they seem to be vibrating but so does a lot of the other metal down there. Anyone have any ideas. Thanks

Here's 4 things to look at: Cage bearing support for the blower, broken motor mount causing the fan to hit the frame, bad start capacitor, loose motor.

Thank you ma0641. We will check those things out. Appreciate the answer.