The noise from the canister indicates that the pump is still likely working but either the impeller is broken, or, that there is a blockage inside the system. The system has a filter for the input side of things which makes it unlikely that there's a solid blockage so the other possibility is an air lock.
I took the canister outside and used a garden hose to force water through from the input line, and watched water exit the outflow line. I then submerged both lines and turned the pump on. It started working quietly just as when I had first purchased it many years ago.
I took it back to my tank, reconnected it, and again it stopped working.
I then dragged my garden hose inside the house, and again forced water through it, and then quickly submerged the input line to stop air entering. It then started working though not as quietly as when I had done this outside. So, it appears that I had an air lock.
I also tried using an aquarium pump to push water through the system but it was simply not strong enough.
If the actual pump had failed I would be looking at replacing the whole unit as repairing just the pump would be too expensive. I've seen some people on youtube successfully place pond pumps on the inlet hose bypassing the canister pump. I'd be interested in knowing what size pond pump would work if that happens to me in the future.