Perhaps the motor brushes are worn out? Unless you hear grinding or knocking noise the bearing should still be OK. Brushes are replaceable if you can use a soldering iron. Beats the alternative of buying a new motor.

I took mine out recently and the blower enclosure was full of leaves. This caused a flapping noise. The blower was also working intermittently. Turns out it had whatever they use for insulation under the dash wrapped around both of the motor shafts inboard of the fan cages and it was binding the whole thing up under current. Apparently that stuff gets sucked up into the squirrel cage and winds itself around the shafts. I wouldn't be surprised if that's the cause of a lot of burned out motors. Brushes were fine so I put a drop of trans fluid on the shafts at the bearing and hit the commutator with some contact cleaner. Works like it should now.

Try jiggling the switch as well, it might be worn out. These blower motors will need for you to check on them every ten years or so. It's not difficult but you do have to remove the wiper to get at it.

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