Loud Humming Coming From (Presumably) Floppy Drive

Floppy drive works? Eject works?

Usually the eject mechanism in the floppy drive gets stuck by the age and hardened grease and chews one plastic gear which would result in non-stop operation of the eject motor.

Click on startup would trigger floppy an eject before boot attempt.

So, did you replace the eject mechanism gear? You must also thoroughly lubricate the other gears and check that everything moves freely.

As the machine is almost 30 years old now, the floppy drive must usually be cleaned and relubricated to restore its proper function. All the rails and other moving stuff should be relubed..

Did you check that the head assembly can move freely on its rails? If not, you would need to put some lithium grease on it. This can also cause the grinding noise when the head is stuck and the actuator would try to move it.

Also the main motor can rub onto something underneath, which would cause grinding noises...