Depending on the exact noise it's making, I'd focus on the motor. If you've got another then swapping this out will confirm this straight away.
If not, try this;
You will be able to rotate the motor shaft by hand and it will tend to stop in fixed locations (where the magnetic fields are equal, i think that's right) Well you should get able 5-6 of these postitions throughout a complete rotation.
For each of these postitions, try starting the motor from a standstill with a very small amount of power. If you get a position that doesn't allow the motor to start, then you could be looking at a dead sensor in the motor. I've had this before and it does cause a fair amount of heat when running and produces a knotchy/noisy feel to the motor.
I think I've explained that OK, if not let me know and I'll try again. :-)
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