If your furnace blower motor is making noise, you will need to determine whether or not you can repair the existing blower motor or if you will need to replace it. There are some things that you will need to consider when making your diagnosis. First of all, with the furnace turned off at the circuit breaker, use a flashlight and make a thorough visual inspection of the blower.
Things that you should be looking for include any damaged parts or other debris that may be rubbing against the fan blades during operation. If there is no visual sign of damage or debris, check the motor for a place to add oil to the motor. Some models are considered “permanently oiled” and will not allow you to add any oil. If you can, add oil and power the furnace on again and listen for the noise. If the noise is gone, make sure to add oil on a regular basis or whenever your blower motor begins making noise again.
If neither of these options fixes your problem you would be best served by calling in a trained service technician who can diagnose the exact problem and determine if furnace blower motor repair is possible. It is quite likely at this stage, however, that you will be beyond the point of repairing your furnace blower motor. If this is the case, discuss the needs of your current furnace (and air conditioner) with the service technician to determine what your best option for a replacement will be.
When your furnace blower motor begins making noise, the best thing that you can do is troubleshoot the problem immediately. Whether or not you will be able to repair the problem by yourself will have a lot to do with regular maintenance and a little bit to do with old fashioned luck.