The Amish yodel. As in yodel-ay-eee-ooo.
Not all Amish, though, and maybe not quite like that.
This is a ‘Swiss Amish‘ practice. Within the Swiss ethnic sub-group, Chad L. Thompson tells us (see Anthropological Linguistics Journal vol. 38 no. 3) it’s mainly done in two settlements that straddle Fort Wayne, Indiana–the Adams County bunch to the south, and to a lesser extent, Allen County to the north.