Most turtles mate underwater, so starting to make vocal sounds might be a poor planned idea.
American Box Turtles are terrestrial turtles (not tortoises) and they apparently make not only calling noises for mating, but also noises during mating. Spiny Turtles are a semi-aquatic turtle that seems to mate on land, as the males are triggered into mating behavior by the rain, they seem to be quiet when mating.
Tortoises are more the ones making sounds during mating. one of the Galapagos Tortoise nicknames are the Elephant Tortoise due to the loud noise it makes when mating.
not sure why it would be called churring, crickets churr... Mating tortoises range from bellowing grunt noises to... "anime girl moaning".