As a former HVAC motor engineer, my professional opinion is that it probably isn't going to fail any time soon. They are designed to last 2000 hours at max speed as a minimum. It could be a couple of things:

1. the shaft could have a burr where the bearings are located.

2. the bearings could have a foreign object in it.

3. the commutator could have sufficient run-out (between bars) to cause many types of ticks, squeaks, buzzes.

4. or the motor sounds like a cricket (known as chirp), this issue requires its own dissertation. Many SAE papers have been written on this condition.

Chirp is a cold (below freezing) weather condition dealing with the friction of the brushes and commutator. Basically there is nothing the end user can do about it (other than change the motor, or run the motor at a higher speed for a few minutes until the noise stops). The only way to eliminate it is to redseign the motor.

My advice it to keep it until you cann't stand the noise anymore.