What is a Noble plum?
A plum called 'Noble' is a type I don't find information about either. There is a patent application for 'Red Noble' in the 1990s by Bradford Farms, California. At that time research on plum-apricot hybrids was promising improved fruit flavors. I don't find it listed for sale now.
Where did your tree come from? That might give the best clues for finding further information.