'Making a noise like a gleed under a door' does not literally = someone singing badly. It *could* refer to that or to a whiney speaking voice, etc. A gleed is a piece of grit. Imagine the noice a piece of grit scraping under a door makes and you'll get the idea.
Lots of dialects, I've found, have the same stories about them. Several accents and dialects claim to be the nearest to old English. I've heard both Black Country folk and Geordies claim that their dialect was once the King's/Queen's English!!!
Glad to see the old Brummie/Black Country thing has been cleared up. It's as annoying as people assuming that all those from the north east are Geordies, or that Canadians are Americans, or New Zealanders are Australians, etc.