Sometimes during blower motor operation you might hear excessive noise. Sometimes this noise is not due to a blower motor problem but occurs because debris is caught inside the blower assembly. During blower operation, this debris causes the blower motor to be noisy. This debris often works its way down into the HVAC system from the vent opening under your windshield wipers at the base of your windshield. With that in mind, try to keep this area free of leaves and debris. This will help prevent something like this from happening.
Another cause is rodent infestation. For some reason, mice like the insulation in the HVAC system. They get in there and make a nice little nest inside your blower motor. I've even found dead mice in blower motors that have caused this issue. The fix is the same no matter what the cause. Remove the blower motor, clean out the debris, reinstall it, then recheck for the noise. It's very effective and just costs you a bit of time. Here's a video on the process.