While it is still making noise. It is still functioning. It could fail tomorrow or keep working. Even if it keeps working it won't cool as effectively and the motor can overheat. It can also draw more power to overcome friction.
It is a critical component for cooling your computer. I would urge you to replace it. When it does completely fail. Your computer will overheat. When it overheats it will shutdown to protect itself. But can be irreversibly damaged.
Also, since this is being used in class. The polite thing to do would be to replace it. So, that you aren't disrupting the lecture with a needlessly noisy computer.