That's really fascinating! My mother had a big operation to remove a growth on a nerve in her inner ear. It left her completely deaf in that ear. A few years later she went on a long train journey, and for weeks afterwards she had a welsh male voice choir singing hymns inside her head. They'd stick on the same hymn for ages, then there'd be a new one. She quite liked it, but it was very disconcerting. I think she'll be glad to know its a recognised thing.

Kris