I had the same on my S2. It is not uncommon. Usually caused by water ingress making the frame damp I think.

As you open or close the door there is what feels like a hard crack/snap type noise as it opens/closes.

As mentioned this is an element of the hinge wearing. It happened on my drivers door with it happening on the passengers door. The drivers door gets a lot more use.

The local well experienced dealership tried to fix it but said back to factory as it is structural wood frame work. Factory did it as part of some other work being done.

Everyone loves a Morgan. Even me, unless it's broken again.