Since I can't hear it I'll just go by your observations. The blower just attaches to the motor shaft so it's not your problem. I'd attach 12 volts directly from the battery and see what the motor sounds like. If it has a laboring, slow to come up to speed, or or squeel sound replace the motor with a new one. Should be able to get one from the parts store. These motors don't wear down the battery when the car is running. The alternator keeps them going.