The trim makes a loud clacking sound when it's running, for that reason. (And the Ethiopian pilots did know the trim was running.)

This is what I mean when the newspaper articles constantly leave out crucial details. You have to read many articles to get an idea of the complete picture.

It doesn't matter that a third pilot figured out what was wrong and what the corrective action should be. Because after he did it, it was known and all the pilots should have known.