Upload & Sell: Off
Maybe pull the film out and try to shoot it dry. Could be that it has been sitting for a long time and needs exercise. That said, the AE-1/AE-1P cameras did have a tendency to develop shutter problems (happened to me with my AE-1P eons ago). When I worked in photo retail, we took in camera trade-ins and always checked the Canon A series cameras for 'shutter squeal,' which was a telltale sign of likely problems.
It might just need an overhaul, but it would be cheaper to buy one that is problem free.