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One thing to always try,,, go ahead and pull the brushes back out,, and then spin the motor by hand,, If the bearings are bad,, you will hear them,, not very loud, but you can hear them. They usualy wont get loud until the motor is up to speed,, then they make all sorts of bad noises. Also to remember, if you replace the bearings,,always try to get good bearings,,not the chinese replacement bearings,,I have had more than one motor get bearing noise after a month of replacing them with cheap bearings,,Victor