Hey singertobe,
I don't think these really shed any light on different Rhiannon pronunciations but they are Welsh Rhiannon songs that you may be interested in hearing;
https://www.youtube.com/watch?v=5dJo84QtaD8
https://www.youtube.com/watch?v=9wckHKz02Ho
Also, this is Welsh comedian Rhod Gilbert on learning the Welsh language;
https://www.youtube.com/watch?v=qvSc...vScUgHcA8Y#t=5
Also, Ali G (Sacha Baron Cohen) learning Welsh;
https://www.youtube.com/watch?v=3WnFW5mgPbk