Lighting, Light Fixtures, Ceiling and Exhaust Fans - Attic fan broke down: several questions

I have a 10-yr-old attic exhaust fan that recently broke down. I am not sure what's wrong. When I turn on the switch, sometimes I get humming coming from the motor (I think) and sometimes I do not. At one moment when I was looking at it and was not doing anything in particular, the humming suddenly started, the fan did maybe a 1/2 circle rotation then it stopped and a few seconds later the humming stopped as well.

A couple of months ago we had some insulation work done in the attic. The contractor installed special soft screens that cover the entire attic area and are supposed to prevent our upper level rooms from getting hot in the summer. Is it possible that these screens somehow restricted air flow forcing the fan to work harder? Also, one thing that I noticed when I sat in the attic is that there is an "outgoing" window in front of the fan where the hot air gets pushed out. But are we also supposed to have an "incoming" window on the opposite wall? If not, then is the airflow restricted too much by the new barriers? Finally, what do you think is wrong with the fan and is it worth repairing or do we need to replace it?

Thanks much!

Given the age of the fan I think it might be time to replace it.

Yes, you need makeup air to counter the air that is being exhausted by the fan. Soffit vents or a gable vents would work.

Sounds like the barrings or some other part is more than the motor can turn (as in the motor is wore out). The humming is the motor trying to spin but it can't. The humming stops because there is an overload in the motor so it can't overheat. When the motor cools it kicks back in, tries to run and gets hot again and trips the overload.