HP 41 Card reader problem

[Hans Brueggemann]

that sound could be a reaction of the internal DC/DC converter to an overload condition.
fortunately, the motor is "weak enough", so it is not capable of damaging the plastic gear of the drive roller. you should start from the beginning and dismantle card reader and assemble it again, but without having the drive roller assembly installed. then, insert the card and check whether the motor spins up. if you still hear the high pith whine and the motor doesn't start, the motor's rotor is probably stuck with congested lubricant, or the commutator inside the motor is somehow damaged.