But wait -- they're in Amish dress!
That was my experience this evening on the way home from work.
There's an Amish-run bulk food store on the way home that I visit from time to time for baking supplies. Tonight as I entered the building I heard singing -- faint female voices singing a capella, in an unusual but pleasing harmony reminiscent of Southern shaped note singing.
Then the storeroom door opened and a young girl came out, humming. Behind her were about a half-dozen other teenage girls, singing "Hark! The Herald Angels Sing." They smiled but quickly shut the door.
The Amish don't often share their singing talents with their English neighbors, so it was a real treat to hear them.